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| -rw-r--r-- | doc/build/orm/relationships.rst | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/doc/build/orm/relationships.rst b/doc/build/orm/relationships.rst index e98ec657c..a2e0bd590 100644 --- a/doc/build/orm/relationships.rst +++ b/doc/build/orm/relationships.rst @@ -1400,6 +1400,50 @@ unit of work searches only through the current identity map for objects that may be referencing the one with a mutating primary key, not throughout the database. + +Specifying Joins Across Multiple Tables +--------------------------------------- + +Joins across multiple tables is done by specifying the +``primaryjoin``, ``secondaryjoin``, and ``secondary`` +parameters of the :func:`.relationship`. + +A typical example may look like:: + + class A(Base): + __tablename__ = 'a' + + id = Column(Integer, primary_key=True) + b_id = Column(Integer, ForeignKey('b.id')) + + c_via_secondary = relationship( + 'C', + # NOTE: secondary is the **table name** of B + secondary='b', + primaryjoin='A.b_id == B.id', + secondaryjoin='C.id == B.c_id' + ) + + class B(Base): + __tablename__ = 'b' + + id = Column(Integer, primary_key=True) + c_id = Column(Integer, ForeignKey('c.id')) + + class C(Base): + __tablename__ = 'c' + id = Column(Integer, primary_key=True) + + +The relationship can be accessed the same as any other relationship:: + + a1 = sess.query(A).first() + + print(a1.c_via_secondary) + + + + Relationships API ----------------- |