SQLBuilder

Contents

A number of variables from SQLBuilder are included with from sqlobject import * -- see the relevant SQLObject documentation for more. Its functionality is also available through the special q attribute of SQLObject classes.

SQLExpression

SQLExpression uses clever overriding of operators to make Python expressions build SQL expressions -- so long as you start with a Magic Object that knows how to fake it.

With SQLObject, you get a Magic Object by accessing the q attribute of a table class -- this gives you an object that represents the field. All of this is probably easier to grasp in an example:

>>> from sqlobject.sqlbuilder import *
>>> person = table.person
# person is now equivalent to the Person.q object from the SQLObject
# documentation
>>> person
person
>>> person.first_name
person.first_name
>>> person.first_name == 'John'
person.first_name = 'John'
>>> name = 'John'
>>> person.first_name != name
person.first_name <> 'John'
>>> AND(person.first_name == 'John', person.last_name == 'Doe')
(person.first_name = 'John' AND person.last_name = 'Doe')

Most of the operators work properly: <, >, <=, >=, !=, ==, +, -, /, *, **, %. However, and, or, and not do not work. You can use &, |, and ~ instead -- but be aware that these have the same precedence as multiplication. So:

# This isn't what you want:
>> person.first_name == 'John' & person.last_name == 'Doe'
(person.first_name = ('John' AND person.last_name)) = 'Doe')
# This is:
>> (person.first_name == 'John') & (person.last_name == 'Doe')
((person.first_name = 'John') AND (person.last_name == 'Doe'))

SQLBuilder also contains the functions AND, OR, and NOT which also work -- I find these easier to work with. AND and OR can take any number of arguments.

You can also use .startswith() and .endswith() on an SQL expression -- these will translate to appropriate LIKE statements and all % quoting is handled for you, so you can ignore that implementation detail. There is also a LIKE function, where you can pass your string, with % for the wildcard, as usual.

If you want to access an SQL function, use the func variable, like:

>> person.created < func.NOW()

To pass a constant, use the const variable which is actually an alias for func.

SQL statements

SQLBuilder implements objects that execute SQL statements. SQLObject uses them internally in its higher-level API, but users can use this mid-level API to execute SQL queries that are not supported by the high-level API. To use these objects first construct an instance of a statement object, then ask the connection to convert the instance to an SQL query and finally ask the connection to execute the query and return the results. For example, for Select class:

>>> from sqlobject.sqlbuilder import *
>> select = Select(['name', 'AVG(salary)'], staticTables=['employees'],
>>     groupBy='name') # create an instance
>> query = connection.sqlrepr(select) # Convert to SQL string:
>>     # SELECT name, AVG(salary) FROM employees GROUP BY name
>> rows = connection.queryAll(query) # Execute the query
>>     # and get back the results as a list of rows
>>     # where every row is a sequence of length 2 (name and average salary)

Select

A class to build SELECT queries. Accepts a number of parameters, all parameters except items are optional. Use connection.queryAll(query) to execute the query and get back the results as a list of rows.

items:
A string, an SQLExpression or a sequence of strings or SQLExpression's, represents the list of columns. If there are q-values SQLExpression's Select derives a list of tables for SELECT query.
where:
A string or an SQLExpression, represents the WHERE clause.
groupBy:
A string or an SQLExpression, represents the GROUP BY clause.
having:
A string or an SQLExpression, represents the HAVING part of the GROUP BY clause.
orderBy:
A string or an SQLExpression, represents the ORDER BY clause.
join:
A (list of) JOINs (LEFT JOIN, etc.)
distinct:
A bool flag to turn on DISTINCT query.
start, end:
Integers. The way to calculate OFFSET and LIMIT.
limit:
An integer. limit, if passed, overrides end.
reversed:
A bool flag to do ORDER BY in the reverse direction.
forUpdate:
A bool flag to turn on SELECT FOR UPDATE query.
staticTables:
A sequence of strings or SQLExpression's that name tables for FROM. This parameter must be used if items is a list of strings from which Select cannot derive the list of tables.

Insert

A class to build INSERT queries. Accepts a number of parameters. Use connection.query(query) to execute the query.

table:
A string that names the table to INSERT into. Required.
valueList:

A list of (key, value) sequences or {key: value} dictionaries; keys are column names. Either valueList or values must be passed, but not both. Example:

>> insert = Insert('person', valueList=[('name', 'Test'), ('age', 42)])
       # or
>> insert = Insert('person', valueList=[{'name': 'Test'}, {'age': 42}])
>> query = connection.sqlrepr(insert)
       # Both generate the same query:
       # INSERT INTO person (name, age) VALUES ('Test', 42)
>> connection.query(query)
values:

A dictionary {key: value}; keys are column names. Either valueList or values must be passed, but not both. Example:

>> insert = Insert('person', values={'name': 'Test', 'age': 42})
>> query = connection.sqlrepr(insert)
       # The query is the same
       # INSERT INTO person (name, age) VALUES ('Test', 42)
>> connection.query(query)

Instances of the class work fast and thus are suitable for mass-insertion. If one needs to populate a database with SQLObject running a lot of INSERT queries this class is the way to go.

Update

A class to build UPDATE queries. Accepts a number of parameters. Use connection.query(query) to execute the query.

table:
A string that names the table to UPDATE. Required.
values:
A dictionary {key: value}; keys are column names. Required.
where:
An optional string or SQLExpression, represents the WHERE clause.

Example:

>> update = Update('person',
>>     values={'name': 'Test', 'age': 42}, where='id=1')
>> query = connection.sqlrepr(update)
       # UPDATE person SET name='Test', age=42 WHERE id=1
>> connection.query(query)

Delete

A class to build DELETE FROM queries. Accepts a number of parameters. Use connection.query(query) to execute the query.

table:
A string that names the table to UPDATE. Required.
where:
An optional string or an SQLExpression, represents the WHERE clause. Required. If you need to delete all rows pass where=None; this is a safety measure.

Example:

>> update = Delete('person', where='id=1')
>> query = connection.sqlrepr(update)
       # DELETE FROM person WHERE id=1
>> connection.query(query)

Union

A class to build UNION queries. Accepts a number of parameters - Select queries. Use connection.queryAll(query) to execute the query and get back the results.

Example:

>> select1 = Select(['min', func.MIN(const.salary)], staticTables=['employees'])
>> select2 = Select(['max', func.MAX(const.salary)], staticTables=['employees'])
>> union = Union(select1, select2)
>> query = connection.sqlrepr(union)
       # SELECT 'min', MIN(salary) FROM employees
       #    UNION
       # SELECT 'max', MAX(salary) FROM employees
>> rows = connection.queryAll(query)

Nested SQL statements (subqueries)

There are a few special operators that receive as parameter SQL statements. These are IN, NOTIN, EXISTS, NOTEXISTS, SOME, ANY and ALL. Consider the following example: You are interested in removing records from a table using deleteMany. However, the criterion for doing so depends on another table.

You would expect the following to work:

>> PersonWorkplace.deleteMany(where=
   ((PersonWorkplace.q.WorkplaceID==Workplace.q.id) &
   (Workplace.q.id==SOME_ID)))

But this doesn't work! However, you can't do a join in a deleteMany call. To work around this issue, use IN:

>> PersonWorkplace.deleteMany(where=
   IN(PersonWorkplace.q.WorkplaceID,
   Select(Workplace.q.id, Workplace.q.id==SOME_ID)))
Get SQLObject at Sourceforge.net. Fast, secure and Free Open Source software downloads