Quick-start Guide / Tutorial — KInterbasDB v3.3.0 documentation

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# Quick-start Guide / Tutorial

This brief tutorial aims to get the reader started by demonstrating elementary usage of KInterbasDB. It is not a comprehensive Python Database API tutorial, nor is it comprehensive in its coverage of anything else.

The numerous advanced features of KInterbasDB are covered in another section of this documentation, which is not in a tutorial format, though it is replete with examples.

## Connecting to a Database

Example 1

A database connection is typically established with code such as this:

    import kinterbasdb

    # The server is named 'bison'; the database file is at '/temp/test.db'.
    con = kinterbasdb.connect(dsn='bison:/temp/test.db', user='sysdba', password='pass')

    # Or, equivalently:
    con = kinterbasdb.connect(
        host='bison', database='/temp/test.db',
        user='sysdba', password='pass'
      )

Example 2

Suppose we want to connect to the database in SQL Dialect 1 and specifying UTF-8 as the character set of the connection:

    import kinterbasdb

    con = kinterbasdb.connect(
        dsn='bison:/temp/test.db',
        user='sysdba', password='pass',
        dialect=1, # necessary for all dialect 1 databases
        charset='UTF8' # specify a character set for the connection
      )

## Executing SQL Statements

For this section, suppose we have a table defined and populated by the following SQL code:

    create table languages
    (
      name               varchar(20),
      year_released      integer
    );

    insert into languages (name, year_released) values ('C',        1972);
    insert into languages (name, year_released) values ('Python',   1991);

Example 1

This example shows the simplest way to print the entire contents of the languages table:

    import kinterbasdb

    con = kinterbasdb.connect(dsn='/temp/test.db', user='sysdba', password='masterkey')

    # Create a Cursor object that operates in the context of Connection con:
    cur = con.cursor()

    # Execute the SELECT statement:
    cur.execute("select * from languages order by year_released")

    # Retrieve all rows as a sequence and print that sequence:
    print cur.fetchall()

Sample output:

    [('C', 1972), ('Python', 1991)]

Example 2

Here’s another trivial example that demonstrates various ways of fetching a single row at a time from a SELECT-cursor:

    import kinterbasdb

    con = kinterbasdb.connect(dsn='/temp/test.db', user='sysdba', password='masterkey')

    cur = con.cursor()
    SELECT = "select name, year_released from languages order by year_released"

    # 1. Iterate over the rows available from the cursor, unpacking the
    # resulting sequences to yield their elements (name, year_released):
    cur.execute(SELECT)
    for (name, year_released) in cur:
        print '%s has been publicly available since %d.' % (name, year_released)

    # 2. Equivalently:
    cur.execute(SELECT)
    for row in cur:
        print '%s has been publicly available since %d.' % (row[0], row[1])

    # 3. Using mapping-iteration rather than sequence-iteration:
    cur.execute(SELECT)
    for row in cur.itermap():
        print '%(name)s has been publicly available since %(year_released)d.' % row

Sample output:

    C has been publicly available since 1972.
    Python has been publicly available since 1991.
    C has been publicly available since 1972.
    Python has been publicly available since 1991.
    C has been publicly available since 1972.
    Python has been publicly available since 1991.

Example 3

The following program is a simplistic table printer (applied in this example to languages):

    import kinterbasdb as k

    TABLE_NAME = 'languages'
    SELECT = 'select * from %s order by year_released' % TABLE_NAME

    con = k.connect(dsn='/temp/test.db', user='sysdba', password='masterkey')

    cur = con.cursor()
    cur.execute(SELECT)

    # Print a header.
    for fieldDesc in cur.description:
        print fieldDesc[k.DESCRIPTION_NAME].ljust(fieldDesc[k.DESCRIPTION_DISPLAY_SIZE]) ,
    print # Finish the header with a newline.
    print '-' * 78

    # For each row, print the value of each field left-justified within
    # the maximum possible width of that field.
    fieldIndices = range(len(cur.description))
    for row in cur:
        for fieldIndex in fieldIndices:
            fieldValue = str(row[fieldIndex])
            fieldMaxWidth = cur.description[fieldIndex][k.DESCRIPTION_DISPLAY_SIZE]

            print fieldValue.ljust(fieldMaxWidth) ,

        print # Finish the row with a newline.

Sample output:

    NAME                 YEAR_RELEASED
    ------------------------------------------------------------------------------
    C                    1972
    Python               1991

Example 4

Let’s insert more languages:

    import kinterbasdb

    con = kinterbasdb.connect(dsn='/temp/test.db', user='sysdba', password='masterkey')

    cur = con.cursor()

    newLanguages = [
        ('Lisp',  1958),
        ('Dylan', 1995),
      ]

    cur.executemany("insert into languages (name, year_released) values (?, ?)",
        newLanguages
      )

    # The changes will not be saved unless the transaction is committed explicitly:
    con.commit()

Note the use of a parameterized SQL statement above. When dealing with repetitive statements, this is much faster and less error-prone than assembling each SQL statement manually. (You can read more about parameterized SQL statements in the section on Prepared Statements.)

After running Example 4, the table printer from Example 3 would print:

    NAME                 YEAR_RELEASED
    ------------------------------------------------------------------------------
    Lisp                 1958
    C                    1972
    Python               1991
    Dylan                1995

## Calling Stored Procedures

Firebird supports stored procedures written in a proprietary procedural SQL language. Firebird stored procedures can have input parameters and/or output parameters. Some databases support input/output parameters, where the same parameter is used for both input and output; Firebird does not support this.

It is important to distinguish between procedures that return a result set and procedures that populate and return their output parameters exactly once. Conceptually, the latter “return their output parameters” like a Python function, whereas the former “yield result rows” like a Python generator.

Firebird’s server-side procedural SQL syntax makes no such distinction, but client-side SQL code (and C API code) must. A result set is retrieved from a stored procedure by SELECT`ing from the procedure, whereas output parameters are retrieved with an `EXECUTE PROCEDURE statement.

To retrieve a result set from a stored procedure with KInterbasDB, use code such as this:

    cur.execute("select output1, output2 from the_proc(?, ?)", (input1, input2))

    # Ordinary fetch code here, such as:
    for row in cur:
        ... # process row

    con.commit() # If the procedure had any side effects, commit them.

To execute a stored procedure and access its output parameters, use code such as this:

    cur.callproc("the_proc", (input1, input2))

    # If there are output parameters, retrieve them as though they were the
    # first row of a result set.  For example:
    outputParams = cur.fetchone()

    con.commit() # If the procedure had any side effects, commit them.

This latter is not very elegant; it would be preferable to access the procedure’s output parameters as the return value of Cursor.callproc(). The Python DB API specification requires the current behavior, however.

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