InsertFromSelect with columns support

[Diego Woitasen]

Hi,

  This is working version of InsertFromSelect with columns support. Works for me, but I could be useful for somebody else. And also I want to heart other opinions about this.

In SQL there is no way to do an "INSERT... SELECT". If you want to do it without using raw SQL in several places of your code you can create custom SQL compilation.

There is an example about how to do "INSERT...SELECT" in [SA documentation][1]. This example doesn't support column in the INSERT part of the sentence, some thing like: INSERT into table(col1, col2)...".

I've modified the example to that, this support table ("INSERT INTO table (SELECT...)") or columns ("INSERT INTO table (col1, col2) (SELECT...)".

Please, have a look an comment :)

    from sqlalchemy.sql.expression import Executable, ClauseElement

    from sqlalchemy.ext.compiler import compiles

    

    class InsertFromSelect(Executable, ClauseElement):

        def __init__(self, insert_spec, select):

            self.insert_spec = insert_spec

            self.select = select

    

    @compiles(InsertFromSelect)

    def visit_insert_from_select(element, compiler, **kw):

        if type(element.insert_spec) == list:

            columns = []

            for column in element.insert_spec:

                if element.insert_spec[0].table != column.table:

                    raise Exception("Insert columns must belong to the same table")

                columns.append(compiler.process(column, asfrom=True))

    

            table = compiler.process(element.insert_spec[0].table)

            columns = ", ".join(columns)

    

            sql = "INSERT INTO %s (%s) (%s)" % (

                    table, columns,

                    compiler.process(element.select))

    

        else:

            sql = "INSERT INTO %s (%s)" % (

                    compiler.process(element.insert_spec, asfrom=True),

                    compiler.process(element.select))

    

        return sql

Example of its use with columns:

    InsertFromSelect([dst_table.c.col2, dst_table.c.col1], select([src_table.c.col1, src_table.c.col1]))

Example of its use only with a table:

    InsertFromSelect(dst_table, select(src_table]))

  [1]: http://docs.sqlalchemy.org/en/rel_0_7/core/compiler.html#compiling-sub-elements-of-a-custom-expression-construct