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| -rw-r--r-- | doc/build/content/session.txt | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/doc/build/content/session.txt b/doc/build/content/session.txt index cae0339ea..a81b518ab 100644 --- a/doc/build/content/session.txt +++ b/doc/build/content/session.txt @@ -439,6 +439,25 @@ Finally, for MySQL, Postgres, and soon Oracle as well, the session can be instru # before committing both transactions sess.commit() +## Embedding SQL Insert/Update Expressions into a Flush {@name=flushsql} + +This feature allows the value of a database column to be set to a SQL expression instead of a literal value. It's especially useful for atomic updates, calling stored procedures, etc. All you do is assign an expression to an attribute: + + {python} + class SomeClass(object): + pass + mapper(SomeClass, some_table) + + someobject = session.query(SomeClass).get(5) + + # set 'value' attribute to a SQL expression adding one + someobject.value = some_table.c.value + 1 + + # issues "UPDATE some_table SET value=value+1" + session.commit() + +This works both for INSERT and UPDATE statements. After the flush/commit operation, the `value` attribute on `someobject` gets "deferred", so that when you again access it the newly generated value will be loaded from the database. This is the same mechanism at work when database-side column defaults fire off. + ## Using SQL Expressions with Sessions {@name=sql} SQL constructs and string statements can be executed via the `Session`. You'd want to do this normally when your `Session` is transactional and youd like your free-standing SQL statements to participate in the same transaction. |