erlang odbc2.0

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ErlangODBCapplication

version2.0



Typ eset in LATEX from SG ML source using the D ocBuilder-0.9.7 D ocument Sy stem.



Contents

1 ErlangODBC User’sGuide 1

1.1 Int roduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 P urpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.2 P rereq uisit es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.3 About O D BC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.4 Ab out t he Erlang O D B C applicat io n . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 G et ting st art ed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.1 Set ting things up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.2 U sing t he Erlang AP I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3 D at abases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3.1 D at abases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3.2 D a tabase independence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3.3 D at a t ypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3.4 Batch handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.4 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.4.1 Strat egy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.4.2 The w hole pict ure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2 ErlangODBC ReferenceManual 13

2.1 odbc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

List of Figures 23

List of Tables 25

iiiErlang O D BC application



iv Erlang O D BC application



Chapter 1

Erlang ODBC User’s Guide

The ErlangODBC Application provides an interface for accessing relationa l SQ L-dat abases from Erlang.

1.1 Introduction

1.1.1 Purpose

The purpose of the Erlang O D BC application is to provide the programm er with an O D BC interface

tha t ha s a Erlang/O TP t ouch and feel. So t hat the program mer may concentrat e on solving his/her

actual problem instead of struggling with pointers and m emory allocation w hich is not very relevant for

Erlang. This user guide will give you some information about technical issues and provide some

examples of how to use the Erlang ODBC interface.

1.1.2 Prerequisites

It is assumed that the reader is familiar w ith t he Erlang programm ing language, concepts of OTP and

has a ba sic understanding of relational databa ses and SQ L.

1.1.3 About ODBC

O pen D atabase C onnectivity (OD BC ) is a Microsoft standard for accessing relational databases that has

become w idely used. The O D BC standard provides a c-level application programming interface (API)

for da tabase access. It uses Structured Q uery Language (SQL ) as its datab ase access language.

1.1.4 About the Erlang ODBC application

Provides an Erlang interface to com municate w ith relational SQ L-datab ases. It is built o n top of

Microsofts O D BC interface and therefore requires that you have an OD BC driver to the datab ase that

you w ant t o connect t o. The Erlang OD BC application is designed using the version 3.0 of the

O D BC -standard, how ever using the option

scrollable cursors, off

for a connection has been

know n to make it w ork for at least some 2.X drivers.

1Erlang O D BC application



Chapter 1: Erlang ODBC User’s Guide

1.2 Getting started

1.2.1 Setting things up

As the Erlang O D BC application is dependent on t hird party products there are a few ad ministrative

things that needs to be done before you can get t hings up and running.

The first t hing you need to do, is to m ake sure you have an O D BC driver installed for t he databa se

that you want to access. Both the client machine where you plan to run your erlang node and the

server machine running the da tabase needs the the O D BC driver. (In some cases the client and

the server may be the same machine).

Secondly you m ight need to set environment variables and pa ths to appropriate values. This may

differ a lot betw een different os’s, dat abases and O D BC drivers. This is a confi guration problem

related t o t he third party product and hence we can not give you a standard solution in this guide.

The Erlang O D BC application consists of both Erlang and C code. The C code is delivered as a

precompiled executable for w indows and solaris in the commercial build. In th e open source

distribution it is built the same w ay as all ot her application using configure and make. You m ay

w ant t o provide the the pat h t o yo ur O D BC libraries using –w ith-odbc= PATH .

Note:The Erlang O D BC application should run on all Unix dialects including Linux, Window s 2000,

Window s X P and N T. But currently it is only t ested f or Solaris, Windows 2000, Windows X P and

NT.

1.2.2 Using the Erlang API

The follow ing dialog w ithin the Erlang shell illustrates the functionality o f t he Erlang O D BC interface.The table used in the example does not have any relevance to anything that exist in reality, it is just a

simple example. The example was created using sqlserver 7.0 with servicepack 1 as database and

the ODBC driver for sqlserver w ith version 2000.80.194.00.

1 > application:start(odbc).

ok

C onnect to the database

2 > {ok, Ref} = odbc:connect("DSN=sql-server;UID=aladin;PWD=sesame", []).

{ok,<0.342.0>}

C reate a table

3 > odbc:sql_query(Ref, "CREATE TABLE EMPLOYEE (NR integer,

FIRSTNAME char varying(20), LASTNAME char varying(20), GENDER char(1),

PRIMARY KEY(NR))").

{updated,undefined}

Insert some data

2 Erlang O D BC application



1.2: Getting started

4 > odbc:sql_query(Ref, "INSERT INTO EMPLOYEE VALUES(1, ’Jane’, ’Doe’, ’F’)").

{updated,1}

C heck what data types the dat abase assigned for t he columns. H opefully t his is not a surprise, some

times it can be! These are the data types that y ou should use if you w ant t o do a parameterized query.

5 > odbc:describe_table(Ref, "EMPLOYEE").

{ok, [{"NR", sql_integer},

{"FIRSTNAME", {sql_varchar, 20}},

{"LASTNAME", {sql_varchar, 20}}

{"GENDER", {sql_char, 1}}]}

Use a parameterized query to insert many row s in one go.

6 > odbc:param_query(Ref,"INSERT INTO EMPLOYEE (NR, FIRSTNAME, "

"LASTNAME, GENDER) VALUES(?, ?, ?, ?)",

[{sql_integer,[2,3,4,5,6,7,8]},

{{sql_varchar, 20},

["John", "Monica", "Ross", "Rachel",

"Piper", "Prue", "Louise"]},

{{sql_varchar, 20},

["Doe","Geller","Geller", "Green",

"Halliwell", "Halliwell", "Lane"]},

{{sql_char, 1}, ["M","F","M","F","F","F","F"]}]).

{updated, 7}

Fetch all data in the tab le employee

7> odbc:sql_query(Ref, "SELECT * FROM EMPLOYEE").

{selected,["NR","FIRSTNAME","LASTNAME","GENDER"],

[{1,"Jane","Doe","F"},{2,"John","Doe","M"},

{3,"Monica","Geller","F"},

{4,"Ross","Geller","M"},

{5,"Rachel","Green","F"},

{6,"Piper","Halliwell","F"},

{7,"Prue","Halliwell","F"},

{8,"Louise","Lane","F"}]]}

Associate a result set containg t he w hole table EMPLOYEE to t he connection. The number of row s in the

result set is returned.

8 > odbc:select_count(Ref, "SELECT * FROM EMPLOYEE").{ok,8}

You can always traverse the result set sequential by using next

9 > odbc:next(Ref).

{selected,["NR","FIRSTNAME","LASTNAME","GENDER"],[{1,"Jane","Doe","F"}]}

10 > odbc:next(Ref).

{selected,["NR","FIRSTNAME","LASTNAME","GENDER"],[{2,"John","Doe","M"}]}





If your driver supports scrollable cursors you have a little more freedom, and can do thigs like this.

11 > odbc:last(Ref).

{selected,["NR","FIRSTNAME","LASTNAME","GENDER"],[{8,"Louise","Lane","F"}]}

12 > odbc:prev(Ref).{selected,["NR","FIRSTNAME","LASTNAME","GENDER"],[{7,"Prue","Halliwell","F"}]}

13 > odbc:first(Ref).

{selected,["NR","FIRSTNAME","LASTNAME","GENDER"],[{1,"Jane","Doe","F"}]}

14 > odbc:next(Ref).

{selected,["NR","FIRSTNAME","LASTNAME","GENDER"],[{2,"John","Doe","M"}]}

Fetch th e fi elds FIRSTNAME an d NR for all female employees

15 > odbc:sql_query(Ref, "SELECT FIRSTNAME, NR FROM EMPLOYEE WHERE GENDER = ’F’").

{selected,["FIRSTNAME","NR"],[{"Jane",1},

{"Monica",3},

{"Rachel",5},

{"Piper",6},

{"Prue",7},

{"Louise",8}]}

Fetch th e fi elds FIRSTNAME an d NR for all female employees and sort them on t he field FIRSTNAME .

16 > odbc:sql_query(Ref, "SELECT FIRSTNAME, NR FROM EMPLOYEE WHERE GENDER = ’F’

ORDER BY FIRSTNAME").

{selected,["FIRSTNAME","NR"],[{"Jane",1},

{"Louise",8},

{"Monica",3},

{"Piper",6},

{"Prue",7},

{"Rachel",5}]}

Associate a result set t hat contains the fi elds FIRSTNAME and NR for all female employees to t he

connection. The number of rows in the result set is returned.

17 > odbc:select_count(Ref, "SELECT FIRSTNAME, NR FROM EMPLOYEE WHERE GENDER = ’F’").

{ok,6}

A few more w ays of retriving parts of t he result set w hen the driver supports scrollable cursors. Not e

that next w ill w ork even w ithout support fo r scrollable cursors.

18 > odbc:select(Ref, {relative, 2}, 3).

{selected,["FIRSTNAME","NR"],[{"Monica",3},{"Rachel",5},{"Piper",6}]}

19 > odbc:select(Ref, next, 2).

{selected,["FIRSTNAME","NR"],[{"Prue",7},{"Louise",8}]}




1.3: Databases

20 > odbc:select(Ref, {absolute, 1}, 2).

{selected,["FIRSTNAME","NR"],[{"Jane",1},{"Monica",3}]}

21 > odbc:select(Ref, next, 2).

{selected,["FIRSTNAME","NR"],[{"Rachel",5},{"Piper",6}]}

22 > odbc:select(Ref, {absolute, 1}, 4).

{selected,["FIRSTNAME","NR"],

[{"Jane",1},{"Monica",3},{"Rachel",5},{"Piper",6}]}

Select, using a parameterized query.

23 > odbc:param_query(Ref, "SELECT * FROM EMPLOYEE WHERE GENDER=?",

[{{sql_char, 1}, ["M"]}]).

{selected,["NR","FIRSTNAME","LASTNAME","GENDER"],

[{2,"John", "Doe", "M"},{4,"Ross","Geller","M"}]}

D elete the table EMPLOYEE.

24 > odbc:sql_query(Ref, "DROP TABLE EMPLOYEE").

{updated,undefined}

Shut down the connection.

25 > odbc:disconnect(Ref).

ok

Shut down the application.

26 > application:stop(odbc).=INFO REPORT==== 7-Jan-2004::17:00:59 ===

application: odbc

exited: stopped

type: temporary

ok

1.3 Databases

1.3.1 Databases

If you need t o a ccess a relational database such as sqlserver, mysql, postgres, oracle, cybase etc.

from your erlang application using the Erlang O D BC interface is a good w ay to go about it.

The Erlang O D BC application should w ork for any relational database that ha s an O D BC driver. But

currently it is only regularly tested for sqlserver and postgres.





1.3.2 Database independence

The Erlang OD BC interface is in principal dat abase independent, e.i. a n erlang program using the

interface could be run w ithout changes towa rds different da tabases. But as SQ L is used it is alas

possible to w rite database dependent programs. Even though SQ L is an ANSI-standard meant to be

datab ase independent, different da tabases have proprietary extensions to SQ L d efining their ow n dat a

types. If you keep to the ANSI data types you will minimize the problem. But unfortunately there is noguarantee that all databa ses actually t reats the ANSI data types equivalently. For instance an installation

of Oracle Enterprise release 8.0.5.0.0 for unix will accept that you create a table column with

the ANSI data type integer, but w hen retrinving values from th is column t he driver reports that it is

of type SQL DECIMAL(0, 38) and not SQL INTEGER as you may have expected.

Another obstacle is that some drivers do not support scrollable cursors w hich has the effect t hat the

only way to traverse the result set is sequentially, with next, from the first row to the last, and once you

pass a row you can not go back. This means that some functions in the interface w ill not w ork together

with certain drivers. A similar problem is that not all drivers support “row count” for select queries,

hence resulting in that the function select count/[3,4] w ill return

ok, undefined

instead of

ok,

NrRows

where NrRows is the number of row s in the result set.

1.3.3 Data types

The following is a list o f the ANSI dat a t ypes. For details turn to t he ANSI standard d ocumentation.

Usage of ot her data types is of course possible, but you should be aw are that this makes your

application dependent o n the da tabase you a re using at the mom ent.

CHARACTER (size), CHAR (size)

NU MERIC (precision, scale), D EC IMAL (precision, scale), D EC (precision, scale ) precision -

tot al number o f d igits, scale - total number of decimal places

INTEG ER, INT, S MALLIN T

FLOAT (precision)

REAL

D O U B L E P RECIS IO N

C H ARAC TER VARYING (size), C H AR VARYING (size)

When inputing data using sql query/[2,3] the values w ill alway s be in string format as they are part o f

an SQL-query. Example:

odbc:sql_query(Ref, "INSERT INTO TEST VALUES(1, 2, 3)").

Note:Note that w hen the value of the data to input is a string, it has to be q uoted w ith ’. Example:

odbc:sql_query(Ref, "INSERT INTO EMPLOYEE VALUES(1, ’Jane’, ’Doe’, ’F’)").

You may also input dat a using param query/[3,4] [page 19] and t hen the input dat a w ill have the

Erlang type corresponding to t he OD BC type of the column.See O D BC to Erlang mapping [page 6]





1.3.4 Batch handling

G rouping of SQ L q ueries can be d esirable in order to reduce netw ork traffic. Another benefit can be

that the data source sometimes can optimize execution of a batch of SQL queries.

Explicit batches an procedures described below will result in multiple results being returned from

sql query/[2,3]. w hile w ith parameterized q ueries only one result w ill be returned from

param q uery/[2,3].

Explicit batches

The mo st basic form of a b atch is created by semicolons separated SQ L q ueries, for exam ple:

"SELECT * FROM FOO; SELECT * FROM BAR" or

"INSERT INTO FOO VALUES(1,’bar’); SELECT * FROM FOO"

Procedures

D ifferent dat abases may also support creating of procedures that contains more than one SQ L q uery.For exam ple, th e follow ing SQ LServer-specific sta tem ent creates a procedure tha t ret urns a result set

containing information about employees that w ork at t he department and and a result set listing the

customers of that department.

CREATE PROCEDURE DepartmentInfo (@DepartmentID INT) AS

SELECT * FROM Employee WHERE department = @DepartmentID

SELECT * FROM Customers WHERE department = @DepartmentID

Parameterized queries

To effectively perform a ba tch of similar q ueries, you ca n use parameterized q ueries. This means that

you in your SQ L q uery string will mark the places that usually wo uld contain values with question

marks and then provide lists of values for each parameter. For instance you can use this to insert

multiple rows into the EMPLOYEE table w hile executing only a single SQ L stat ement, for example code

see ”Using the Erlang API” [page 3] section in the “G etting Started” chapter.

1.4 Error handling

1.4.1 Strategy

O n a conceptual level starting a datab ase connection using the Erlang O D BC API is a basic client server

application. The client process uses the API to start and communicate w ith t he server process that

manages the connection. The strategy of the Erlang O D BC application is that programm ing faults in

the application itself will cause the connection process to terminate abnormally.(When a process

terminates abnormally its supervisor will log relevant error reports.) Calls to API functions during or

after t ermination of the connection process, w ill return error, connection closed . Contextual

errors on the other hand w ill not t erminate t he connection it w ill only return error, Reason to the

client, w here Reason may be any erlang term.




1.4: Error handling

Clients

The connection is associated with the process that created it and can only be accessed through it. The

reason for th is is to preserve the semantics of result sets and t ransactions w hen select count /[2,3] is

called or auto commit is turned off. Att empts to use the connection from another process will fail. This

w ill not effect t he connection. O n the o ther hand, if the client process dies the connection w ill be

terminated.

Timeouts

All request made b y t he client to the connection are synchronous. If th e timeout is used and expires the

client process will exit w ith reason timeout. Proably t he right thing to do is let t he client die and

perhaps be restarted by its supervisor. But if the client chooses to catch this timeout, it is a good idea to

wait a little while before trying again. If there are too many consecutive timeouts that are caught the

connection process w ill conclude t hat there is something radically w rong and t erminate the connection.

Gaurds

All API-functions are guarded and if you pass an argument of t he w rong type a runtime error will occur.

All input parameters to internal functions are trusted t o be correct. It is a good programm ing practise to

only distrust input from truly external sources. You are not supposed to catch these errors, it will only

make the code very messy and much m ore complex, w hich introduces more bugs and in t he w orst case

also covers up the actual faults. Put your effort on t esting instead, y ou should trust y our ow n input.

1.4.2 The whole picture

As the Erlang O D BC application relies on third party products and communicates with a d ataba se that

proably runs on an other comput er in the netw ork there are plenty of t hings that might go w rong. To

fully understand t he things that might happen it facilitat e to know the design of the Erlang OD BC

application, hence here follows a short description of the current design.

Note:Please note that design is something, that not necessarily will, but might change in future releases.

While the semantics of the API w ill not change as it is independent of the implementation.





E r l a n g c o

n t r o l p r o c e s s

C - p r o c e s s

E r l a n g c l i e n t

L i n k

C o n n e c t

i o n r e f e r e n c e

r e q u e s t

r e s p o n s e

m

o n i t o r

C o n n e c t r e q

u e s t

S u p e r v i s o r t h r e a d

D a t a b a s e h a n d l e r t h r e a d

r e q u e s t

r e s p o n s e

E r l a n g p o

r t

E x i t s i g n a l p r o p a g a t i o n s h

u t d o w n

E x i t s i g n a l p r o p a g a t i o n

E r l a n g S u p e r v i s o r

Figure 1.1: Architecture of the Erlang odbc application

When you d o application:start(odbc) the o nly thing t hat happens is that a supervisor process is started.

For each call to the API function connect/2 a process is spawned and added a s a child to the Erlang

O D BC supervisor. The supervisors only ta sks are to provide error-log reports, if a child process should

die abnormally, and the possibility to do a cod e change. O nly the client process has the knowledge to

decide if this connection managing process should be restarted.

The erlang connection process spawned by co nnect/2, w ill open a po rt t o a c-process tha t h andles the

communication w ith the data base through Microsoft’s OD BC API. The erlang port w ill be kept open

for exit signal propagation, if something goes wrong in t he c-process and it exits we w ant know as mush

as possible about the reason. The main communication with the c-process is done through sockets. The

C -process consists of tw o threads, t he supervisor thread and the d atabase handler th read. Thesupervisor thread checks for shutdown messages on the supervisor socket and the database handler

thread receives requests and sends answ ers on the d atabase socket. If t he dat abase thread seems to hang

on some data base call, the erlang control process w ill send a shutdow n m essage on the supervisor

socket, in t his case the c-process will exit. If t he c-process crashes/exits it w ill bring the erlang-process

dow n to o and vice versa i.e. t he connection is terminated.




1.4: Error handling

Note:The function connect/2 w ill start the o dbc application if t hat is not already d one. In this case a

supervisor information log w ill be produced stating that the o dbc application w as started as a

temporary application. It is really t he responsibility of the application tha t uses the API too make

sure it is started in the desired way.

Error types

The ty pes of errors that may occur can b e divide into the f ollow ing categories.

Configuration problems - Everything from that the database was not set up right to that the

c-program that should be run th rough the erlang port w as not compiled for your platform.

Errors discovered by t he O D BC driver - If calls to t he O D BC -driver fails due to circumstances

that can not be controlled by t he Erlang O D BC application programm er, an error string will be

dug up from the driver. This string will be the Reason in the

error, Reason

return value.

H ow good t his error message is will of course be driver dependent. Examples of suchcircumstances are trying to insert t he same key tw ice, invalid SQ L-queries and that the d atabase

has gone off line.

C onnection t ermination - If a connection is terminated in an a bnormal w ay, or if yo u try t o use a

connection t hat you h ave already terminated in a normal w ay by calling disconnect/1, th e return

value will be

error, connection closed

. A connection could end abnormally because of an

programming error in the Erlang O D BC application, but also if the O D BC driver crashes.

C ontextual errors - If API functions are used in the w rong context, th e Reason in the error t uple

w ill be a d escriptive atom. For instance if you t ry to call the function last/[1,2] without first

calling select count/[2,3] to associate a result set w ith the connection. If t he OD BC -driver

does not support some functions, or if you d isabled some functionality for a connection and then

try to use it.




Erlang ODBC Reference Manual

Short Summaries

Erlang Module odbc [page 15] – Erlang ODBC application

odbc

The following functions are exported:

commit(Ref, CommitMode) -

[page 16] C omm its or rollbacks a transaction.

commit(Ref, CommitMode, TimeOut) -

ok |

error, Reason

[page 16] C omm its or rollbacks a transaction.

connect(ConnectStr, Options) -

ok, Ref

|

error, Reason

[page 16] O pens a connection to the dat abase.

disconnect(Ref) -

ok |

error, Reason

[page 18] C loses a connection t o a datab ase.

describe table(Ref, Table) -

[page 18] Queries the database to find out the data types of the columns of the

table Table.

describe table(Ref, Table, Timeout) -

ok, Description

|

error,

Reason

[page 18] Queries the database to find out the data types of the columns of the

table Table.

first(Ref) -

[page 18] Returns the first row of t he result set and positions a cursor at this row.

first(Ref, Timeout) -

selected, ColNames, Rows

|

error, Reason

[page 18] Returns the first row of t he result set and positions a cursor at this row.

last(Ref) -

[page 18] Returns the last row of t he result set and positions a cursor at this row.

last(Ref, TimeOut) -


|

error, Reason

[page 18] Returns the last row of t he result set and positions a cursor at this row.

next(Ref) -

[page 19] Returns the next row of the result set relative the current cursor position

and positions the cursor at this row.

next(Ref, TimeOut) -


|

error, Reason

[page 19] Returns the next row of the result set relative the current cursor position

and positions the cursor at this row.




Erlang ODBC Reference Manual

param query(Ref, SQLQuery, Params) -

[page 19] Executes a parameterized SQ L q uery.

param query(Ref, SQLQuery, Params, TimeOut) - ResultTuple | error,

Reason

[page 19] Executes a parameterized SQ L q uery.

prev(Ref) -

[page 19] Returns the previous row of the result set relative the current cursor

position and positions the cursor at this row.

prev(ConnectionReference, TimeOut) -


|

error, Reason

[page 19] Returns the previous row of the result set relative the current cursor

position and positions the cursor at this row.

start() -

[page 20] St arts the o db application.

start(Type) -

ok |

error, Reason

[page 20] St arts the o db application.

stop() -

ok[page 20] Stops the od bc application.

sql query(Ref, SQLQuery) -

[page 20] Executes a SQL query or a batch of SQL queries. If it is a SELECT

query t he result set is returned, on t he format


. For

other q uery types the tuple

updated, NRows

is returned, and for batched queries,

if the driver supports them, this function can also return a list of result tuples.

sql query(Ref, SQLQuery, TimeOut) -

ResultTuple | [ResultTuple]

|

error, Reason

[page 20] Executes a SQL query or a batch of SQL queries. If it is a SELECT

query t he result set is returned, on t he format


. For

other q uery types the tuple

updated, NRows

is returned, and for batched queries,

if the driver supports them, this function can also return a list of result tuples.

select count(Ref, SelectQuery) -

[page 20] Executes a SQ L SELEC T query and associates the result set w ith th e

connection. A cursor is positioned before the fi rst row in the result set and the

tuple

ok, NrRows

is returned.

select count(Ref, SelectQuery, TimeOut) -

ok, NrRows

|

error,

Reason

[page 20] Executes a SQ L SELEC T query and associates the result set w ith th e

connection. A cursor is positioned before the fi rst row in the result set and the

tuple

ok, NrRows

is returned.

select(Ref, Position, N) -

[page 21] Selects Nconsecutive rows of the result set.

select(Ref, Position, N, TimeOut) -


|

error, Reason

[page 21] Selects Nconsecutive rows of the result set.




Erlang ODBC Reference Manual odbc

odbc

Erlang Module

This application provides an Erlang interface to communicate w ith relational

SQ L-databa ses. It is built on top o f Microsofts O D BC interface and th erefore requires

that you have an OD BC driver to the database that you w ant to connect to.

Note:The functions first/[1,2], last/[1,2], next/[1,2], prev[1,2] and

select/[3,4] assumes there is a result set associated w ith t he connection to w ork

on. Calling the function select count/[2,3] associates such a result set with the

connection. Calling select count again will remove the current result set association

and create a new one. C alling a function which do se not operate on an a ssociated

result sets, such as sql query/[2,3], will remove the current result set association.

Alas some drivers only support sequential traversal of the result set, e.i. they do not

support w hat in the O D BC w orld is know n as scrollable cursors. This will have the

effect that functions such as first/[1,2], last/[1,2], prev[1,2], etc w ill return

error, driver does not support function

COMMON DATA TYPESHere follows type definitions that are used by more than one function in the O D BC

API.

Note:The type TimeOut has the default value infinity, so for instance:

commit(Ref, CommitMode) is the same as commit(Ref, CommitMode, infinity). If

the t imeout expires the client w ill exit w ith t he reason timeout.

connection_reference() - as returned by connect/2time_out() = milliseconds() | infinity

milliseconds() = integer() >= 0

common_reason() = connection_closed | term() - some kind of

explanation of what went wrong

string() = list of ASCII characters

col_name() = string() - Name of column in the result set




odbc Erlang ODBC Reference Manual

col_names() - [col_name()] - e.g. a list of the names of the

selected columns in the result set.

row() = {value()} - Tuple of column values e.g. one row of the

result set.

value() = null | term() - A column value.

rows() = [row()] - A list of rows from the result set.

result_tuple() =

{updated, n_rows()} | {selected, col_names(), rows()}

n_rows() = integer() - The number of affected rows for UPDATE,

INSERT, or DELETE queries. For other query types the value

is driver defined, and hence should be ignored.

odbc_data_type() = sql_integer | sql_smallint | sql_tinyint |

{sql_decimal, precison(), scale()} |

{sql_numeric, precison(), scale()} |

{sql_char, size()} | {sql_varchar, size()} | {sql_float, precision()} |

{sql_float, precision()} | sql_real | sql_double | sql_bit | atom()

precision() = integer()

scale() = integer()

size() = integer()

ERROR HANDLING

The error h andling strat egy and possible errors sources are described in t he Erlang

O D BC User’s G uide. [page 8]

Exports

commit(Ref, CommitMode) -

commit(Ref, CommitMode, TimeOut) - ok | error, Reason

Types:

Ref = connection reference()

C ommitMode = commit | rollback

TimeO ut = time out()

Reason = not an explicit commit connection |

process not owner of odbc connection | common reason()

Commits or rollbacks a transaction. Needed on connections where automatic commit is

turned off.

connect(ConnectStr, Options) -

ok, Ref

|

error, Reason

Types:





ConnectStr = string()

An example of a connection

string:"DSN=sql-server;UID=alladin;PWD=sesame"where DSN is your OD BC

D ata So urce Nam e, U ID is a dat abase user id and P WD is the passw ord for that user.

These are usually the attributes required in the connection string, but some drivers

have oth er driver specific attributes, for

example"DSN=Oracle8;DBQ=gandalf;UID=alladin;PWD=sesame"where DBQ is

your TNSN AMES.O RA entry name e.g. some O racle specific confi guration at tribute.

Options = [] | [opt ion()]

All options has default values.

option() =

auto commit, auto commit mode()

|

timeout, milliseconds()

|

tuple row, tuple mode()

|

scrollable cursors, use srollable cursors()

|

trace driver, trace mode()

The default timeout is infinity

auto commit mode() = on | o ff

D efault is on.

tuple mode() = on | o ff

D efault is on. The option is deprecated and should not be used in new code.

use srollable cursors() = on | o ff

D efault is on.

trace mode() = on | o ff

D efault is off.

Ref = connection reference() - should be used to acess the connection.

Reason = port program executable not found | common reason()

O pens a connection to the dat abase. The connection is associated w ith t he process that

created it and can only be accessed t hrough it. This funtion may spaw n new processes

to handle the connection. These processes w ill terminate if the process that created the

connection dies or if y ou call disconnect/1.

If auto mat ic commit mode is turned on, each q uery will be considered as an individual

transaction and will be automaticly commited after it has been executed. If you want

more than one q uery t o be part of t he same transaction the automatic commit m ode

should be turned of f. Then you w ill have to ca ll commit /3 explicitly t o end a

transaction.

As default result sets are returned as a lists of tuples. The TupleMode option still exists

to keep some degree of backwards com patiblity. If t he option is set to off, result sets will

be returned as a lists of lists instead of a lists of tuples.

Scrollable cursors are nice but causes some overhead. For some connections speed

might be m ore important t han fl exible data access and th en you can d isable scrollable

cursor for a connection, limiting the API but gaining speed

If trace mode is turned on this tells the O D BC driver to w rite a trace log to the fi le

SQ L.LO G that is placed in the current directory of t he erlang emulator. Thisinformation may be useful if you suspect there might be a bug in th e erlang OD BC

application, and it might be relevant for you to send this file to our support. Otherwise

you w ill probably not have much use of this.

Note:For more information about the ConnectStr see description of the function

SQ LD riverConnect in [1].





next(Ref) -

next(Ref, TimeOut) - selected, ColNames, Rows | error, Reason

Types:



C olNames = col names()

Rows = rows()

Reason = result set does not exist | process not owner of odbc connection |

common reason()

Returns the next row of the result set relative the current cursor position and positions

the cursor at this row. If the cursor is positioned at the last row of t he result set w hen

this function is called the returned value w ill be

selected, ColNames,[]

e.i. the list

of row values is empty indicating that there is no more data to fetch.

param query(Ref, SQLQuery, Params) -

param query(Ref, SQLQuery, Params, TimeOut) - ResultTuple | error, Reason

Types:


SQ LQ uery = string() - a SQ L q uery w ith parameter ma rkers/place holders in form of

question marks.

Params = [

odbc data type(), [value()]

]


Values = term() - Must b e consistent w ith th e Erlang data type tha t corresponds to

the OD BC data type OD BC D ataType

Executes a parameterized SQ L q uery. For an example see the ”U sing the Erlang API”

[page 3] in the Erlang O D BC User’s G uide.

Note:Use the function describe t able/[2,3] to find out w hich OD BC data t ype that is

expected for each column of t hat table. If a column has a da ta type tha t is described

w ith capital letters, alas it is not currently supported by the param query function.

Too know w hich Erlang data ty pe corresponds to an O D BC data type see the Erlang

to O D BC data typemapping [page 6] in the U ser’s G uide.

prev(Ref) -

prev(ConnectionReference, TimeOut) -


|

error, Reason

Types:



C olNames = col names()

Rows = rows()

Reason = result set does not exist | driver does not support function |

scrollable cursors disabled | process not owner of odbc connection |

common reason()





Returns the previous row of the result set relative the current cursor position and

positions the cursor at this row.

start() -

start(Type) - ok | error, Reason

Types:

Type = permanent | t ransient | temporary

Starts the odbc application. D efault type is temporary. [application(3)]

stop() -

ok

Stops th e odbc application. [application(3)]

sql query(Ref, SQLQuery) -

sql query(Ref, SQLQuery, TimeOut) - ResultTuple | [ResultTuple] | error, Reason

Types:


SQ LQ uery = string() - The string may be compo sed b y several SQ L-queries

separated by a ”;”, this is called a batch.


ResultTuple = result tu ple()

Reason = process not owner of odbc connection | common reason()

Executes a SQL query or a batch of SQL queries. If it is a SELECT query the result set

is returned, o n th e format


. For other query types the

tuple

updated, NRows

is returned, and fo r batch ed q ueries, if the driver supports

them, this function can also return a list of result tuples.

Note:Some drivers may not have the information of the number of affected rows available

and then the return value may be

updated, undefined

.

The list of column names is ordered in the same way as the list of values of a row, e.g.

the fi rst ColName is associated w ith t he fi rst Value in a Row.

select count(Ref, SelectQuery) -

select count(Ref, SelectQuery, TimeOut) -

ok, NrRows

|

error, Reason

Types:


SelectQ uery = string()

SQ L SELECT query.


NrRows = n rows()

Reason = process not owner of odbc connection | common reason()





Executes a SQ L SELEC T query and associates the result set w ith th e connection. A

cursor is positioned before the first row in the result set and the t uple ok, NrRows

is

returned.

Note:Some drivers may not h ave the information of the number of row s in th e result set,

then NrRows w ill have the value undefined.

select(Ref, Position, N) -

select(Ref, Position, N, TimeOut) -


|

error, Reason

Types:


Position = next |

relative, Pos

|

absolute, Pos

Selection strategy, determines at which row in the result set to start the selection.

Pos = integer()Should indicate a row number in the result set. When used together w ith the o ption

relativeit w ill be used as an offset from the current cursor position, w hen used

together w ith the option absoluteit w ill be interpreted as a row number.

N = integer()


Reason = result set does not exist | driver does not support function |

scrollable cursors disabled | process not owner of odbc connection |

common reason()

Selects N consecutive rows of the result set. If Position is next it is semant icly

equivalent of calling next/[1,2]N times. If Position is

relative, Pos

, Pos will be

used as an offset from t he current cursor position to determine the fi rst selected row. IfPosition is

absolute, Pos

, Pos will be the number of the first row selected. After

this function has returned the cursor is positioned at the last selected row. If there is less

then N rows left of t he result set the length of Rows w ill be less than N. If the first row to

select h appens to be beyond the last row of t he result set, the returned value will be

selected, ColNames,[]

e.i. t he list of row values is empty indicating that there is

no more data to fetch.

REFERENCES

[1]: Microsoft O D BC 3.0, Programm er’s Reference and SD K G uide

See also htt p://msdn.microsoft .com /




List of Figures

1. 1 Arch it ect ure o f t he Erla ng o db c a pp lica tio n . . . . . . . . . . . . . . . . . . . . . . . . . . 10




List of Figures




List of Tables

1.1 Mapping of OD BC data types to the Erlang data types returned to the Erlang application. 7

1.2 Mapping of extended O D BC data t ypes to the Erlang data types returned to the Erlang

applicat ion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7




List of Tables




Index of M odules and Functions

Modules are t yped in this way .

Functions are typed in this way.

commit/2

odbc , 16

commit/3

odbc , 16

connect/2

odbc , 16

describe_table/2

odbc , 18

describe_table/3

odbc , 18

disconnect/1

odbc , 18

first/1

odbc , 18

first/2

odbc , 18

last/1

odbc , 18

last/2

odbc , 18

next/1

odbc , 19

next/2odbc , 19

odbc

commit/2, 16

commit/3, 16

connect/2, 16

describe_table/2, 18

describe_table/3, 18

disconnect/1, 18

first/1, 18

first/2, 18

last/1, 18

last/2, 18

next/1, 19

next/2, 19

param_query/3, 19param_query/4, 19

prev/1, 19

prev/2, 19

select/3, 21

select/4, 21

select_count/2, 20

select_count/3, 20

sql_query/2, 20

sql_query/3, 20

start/0, 20

start/1, 20

stop/0, 20

param_query/3

odbc , 19

param_query/4

odbc , 19

prev/1

odbc , 19

prev/2

odbc , 19

select/3odbc , 21

select/4

odbc , 21

select_count/2

odbc , 20

select_count/3

odbc , 20




Index of Modules and Functions

sql_query/2

odbc , 20

sql_query/3

odbc , 20

start/0

odbc , 20

start/1

odbc , 20

stop/0

odbc , 20

erlang odbc2.0

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