Using the Session — SQLAlchemy 2.0.0b1 documentation

Using the Session

The declarative base and ORM mapping functions described at Mapper Configuration are the primary configurational interface for the ORM. Once mappings are configured, the primary usage interface for persistence operations is the Session.

• Session Basics
  • What does the Session do ?
  • Basics of Using a Session
    • Opening and Closing a Session
    • Framing out a begin / commit / rollback block
    • Using a sessionmaker
    • Querying (1.x Style)
    • Querying (2.0 style)
    • Adding New or Existing Items
    • Deleting
    • Flushing
    • Expiring / Refreshing
    • UPDATE and DELETE with arbitrary WHERE clause
    • Auto Begin
    • Committing
    • Rolling Back
    • Closing
  • Session Frequently Asked Questions
    • When do I make a sessionmaker?
    • When do I construct a Session, when do I commit it, and when do I close it?
    • Is the Session a cache?
    • How can I get the Session for a certain object?
    • Is the session thread-safe?
• State Management
  • Quickie Intro to Object States
    • Getting the Current State of an Object
  • Session Attributes
  • Session Referencing Behavior
  • Merging
    • Merge Tips
  • Expunging
  • Refreshing / Expiring
    • What Actually Loads
    • When to Expire or Refresh
• Cascades
  • save-update
  • delete
    • Using delete cascade with many-to-many relationships
    • Using foreign key ON DELETE cascade with ORM relationships
    • Using foreign key ON DELETE with many-to-many relationships
  • delete-orphan
  • merge
  • refresh-expire
  • expunge
  • Controlling Cascade on Backrefs
  • Notes on Delete - Deleting Objects Referenced from Collections and Scalar Relationships
• Transactions and Connection Management
  • Managing Transactions
    • Using SAVEPOINT
    • Session-level vs. Engine level transaction control
    • Explicit Begin
    • Enabling Two-Phase Commit
    • Setting Transaction Isolation Levels / DBAPI AUTOCOMMIT
    • Tracking Transaction State with Events
  • Joining a Session into an External Transaction (such as for test suites)
• Additional Persistence Techniques
  • Embedding SQL Insert/Update Expressions into a Flush
  • Using SQL Expressions with Sessions
  • Forcing NULL on a column with a default
  • Fetching Server-Generated Defaults
    • Case 1: non primary key, RETURNING or equivalent is supported
    • Case 2: non primary key, RETURNING or equivalent is not supported or not needed
    • Case 3: primary key, RETURNING or equivalent is supported
    • Case 4: primary key, RETURNING or equivalent is not supported
  • Using INSERT, UPDATE and ON CONFLICT (i.e. upsert) to return ORM Objects
    • Using PostgreSQL ON CONFLICT with RETURNING to return upserted ORM objects
  • Partitioning Strategies (e.g. multiple database backends per Session)
    • Simple Vertical Partitioning
    • Coordination of Transactions for a multiple-engine Session
    • Custom Vertical Partitioning
    • Horizontal Partitioning
  • Bulk Operations
    • Usage
    • Comparison to Core Insert / Update Constructs
    • ORM Compatibility / Caveats
• Contextual/Thread-local Sessions
  • Implicit Method Access
  • Thread-Local Scope
  • Using Thread-Local Scope with Web Applications
  • Using Custom Created Scopes
  • Contextual Session API
• Tracking queries, object and Session Changes with Events
  • Execute Events
    • Basic Query Interception
    • Adding global WHERE / ON criteria
    • Re-Executing Statements
  • Persistence Events
    • before_flush()
    • after_flush()
    • after_flush_postexec()
    • Mapper-level Events
  • Object Lifecycle Events
    • Transient
    • Transient to Pending
    • Pending to Persistent
    • Pending to Transient
    • Loaded as Persistent
    • Persistent to Transient
    • Persistent to Deleted
    • Deleted to Detached
    • Persistent to Detached
    • Detached to Persistent
    • Deleted to Persistent
  • Transaction Events
  • Attribute Change Events
• Session API
  • Session and sessionmaker()
  • Session Utilities
  • Attribute and State Management Utilities