![]() when the current transaction is committed or rolled back) so The Session automatically expires all instances along transactionīoundaries (i.e. Of the object which already have a value are not re-populated. Which is already present, the same object is returned, and those attributes When an incoming database row has a primary key that matches an object When ORM objects are returned in results, they are also stored in the identity all () # query using orm-columns, also returns tuples results = session. all () # query with multiple classes, returns tuples results = session. In Python this is most fundamentallyĮxpressed using a try: / except: / else: block such as: Will be called so that the transaction is rolled back immediately, before Operations succeed, the mit() method will be called,īut if any exceptions are raised, the Session.rollback() method We will be committing data to the database. “framing” of the transaction within a context manager for those cases where We may also enclose the mit() call and the overall Framing out a begin / commit / rollback block ¶ Parameter is used to disable this behavior. New Session, unless the Session.expire_on_commit If these objects are insteadĭetached, they will be non-functional until re-associated with a ![]() Session are expired, meaning their contents are erased toīe re-loaded within the next transaction. When using a context manager, all objects associated with the Note that after mit() is called, either explicitly or It typically is passed a singleĮngine as a source of connectivity up front. The Session may be constructed on its own or by using the The most basic Session use patterns are presented here. It’s intended that usually, you’d re-associate detached objects withĪnother Session when you want to work with them again, so that theyĬan resume their normal task of representing database state. ![]() Session, and to continue using them, though this practice has itsĬaveats. It is possible to “detach” objects from a Variety of events that will cause objects to re-access the database in order to State on the objects as matching what’s actually in the database, there are a That it maintains as proxy objects to database rows, which are local to the When using a Session, it’s useful to consider the ORM mapped objects The transaction is about to be committed, the Session firstįlushes all pending changes stored in memory to the database. Whenever the database is about to be queried, or when Program, a change event is generated which is recorded by the Such that whenever an attribute or a collection is modified in the Python The ORM objects maintained by a Session are instrumented Transaction remains in effect until the Session is instructed to Session, and then establishes a transaction on that connection. Resource from an Engine that is associated with the Issued or other objects are persisted with it, it requests a connection The Session begins in a mostly stateless form. “only one object with a particular primary key”. Structure that maintains unique copies of each object, where “unique” means Session, inside a structure called the identity map - a data The ORM objects themselves are maintained inside the Interface where SELECT and other queries are made that will return and modify You’ve loaded or associated with it during its lifespan. With the database and represents a “holding zone” for all the objects which In the most general sense, the Session establishes all conversations Session Basics ¶ What does the Session do ? ¶
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