如何在SQLAlchemy的

Question

執行「左外連接」我要執行這個查詢::

select field11, field12 
from Table_1 t1 
left outer join Table_2 t2 ON t2.tbl1_id = t1.tbl1_id 
where t2.tbl2_id is null 

我有這些類在Python：

class Table1(Base): 
    .... 

class Table2(Base): 
    table_id = Column(
     Integer, 
     ForeignKey('Table1.id', ondelete='CASCADE'), 
    ) 
    .... 

如何獲得上述從下面？

Answer 1

q = session.query(Table1.field1, Table1.field2)\ 
    .outerjoin(Table2)\ # use in case you have relationship defined 
    # .outerjoin(Table2, Table1.id == Table2.table_id)\ # use if you do not have relationship defined 
    .filter(Table2.tbl2_id == None) 

應該這樣做，假設field1和field2來自Table1，而您定義的關係：

class Table2(Base): 
    # ... 
    table1 = relationship(Table1, backref="table2s") 

Answer 2

您也可以做到這一點使用SQLAlchemy的核心只有：

session.execute(
    select(['field11', 'field12']) 
    .select_from(
     Table1.join(Table2, Table1.tbl1_id == Table2.tbl1_id, isouter=True)) 
    .where(Table2.tbl2_id.is_(None)) 
)