sqlalchemy:如何通过一个查询连接多个表？

Question

我有以下SQLAlchemy映射类:

class User(Base):
    __tablename__ = 'users'
    email = Column(String, primary_key=True)
    name = Column(String)

class Document(Base):
    __tablename__ = "documents"
    name = Column(String, primary_key=True)
    author = Column(String, ForeignKey("users.email"))

class DocumentsPermissions(Base):
    __tablename__ = "documents_permissions"
    readAllowed = Column(Boolean)
    writeAllowed = Column(Boolean)

    document = Column(String, ForeignKey("documents.name"))

我需要得到一个这样的表user.email = "user@email.com":

email | name | document_name | document_readAllowed | document_writeAllowed

如何使用SQLAlchemy的一个查询请求？以下代码对我不起作用:

result = session.query(User, Document, DocumentPermission).filter_by(email = "user@email.com").all()

谢谢,

Answer 1

试试这个

q = (Session.query(User,Document,DocumentPermissions)
    .filter(User.email == Document.author)
    .filter(Document.name == DocumentPermissions.document)
    .filter(User.email == 'someemail')
    .all())

Answer 2

一个好的风格是设置一些关系和一个主键用于权限(实际上,通常它是为所有设置整数主键的好方式,但无论如何):

class User(Base):
    __tablename__ = 'users'
    email = Column(String, primary_key=True)
    name = Column(String)

class Document(Base):
    __tablename__ = "documents"
    name = Column(String, primary_key=True)
    author_email = Column(String, ForeignKey("users.email"))
    author = relation(User, backref='documents')

class DocumentsPermissions(Base):
    __tablename__ = "documents_permissions"
    id = Column(Integer, primary_key=True)
    readAllowed = Column(Boolean)
    writeAllowed = Column(Boolean)
    document_name = Column(String, ForeignKey("documents.name"))
    document = relation(Document, backref = 'permissions')

然后用连接做一个简单的查询:

query = session.query(User, Document, DocumentsPermissions).join(Document).join(DocumentsPermissions)

Answer 3

正如@letitbee所说,最佳做法是将主键分配给表并正确定义关系以允许正确的ORM查询.话虽如此...

如果您有兴趣按以下方式编写查询:

SELECT
    user.email,
    user.name,
    document.name,
    documents_permissions.readAllowed,
    documents_permissions.writeAllowed
FROM
    user, document, documents_permissions
WHERE
    user.email = "user@email.com";

然后你应该去做类似的事情:

session.query(
    User, 
    Document, 
    DocumentsPermissions
).filter(
    User.email == Document.author
).filter(
    Document.name == DocumentsPermissions.document
).filter(
    User.email == "user@email.com"
).all()

相反,如果你想做类似的事情:

SELECT 'all the columns'
FROM user
JOIN document ON document.author_id = user.id AND document.author == User.email
JOIN document_permissions ON document_permissions.document_id = document.id AND document_permissions.document = document.name

然后你应该做的事情:

session.query(
    User
).join(
    Document
).join(
    DocumentsPermissions
).filter(
    User.email == "user@email.com"
).all()

关于那个的一点说明......

query.join(Address, User.id==Address.user_id) # explicit condition
query.join(User.addresses)                    # specify relationship from left to right
query.join(Address, User.addresses)           # same, with explicit target
query.join('addresses')                       # same, using a string

有关更多信息,请访问文档.

Answer 4

扩展Abdul的答案，您可以KeyedTuple通过连接列来获取而不是离散的行集合：

q = Session.query(*User.__table__.columns + Document.__table__.columns).\
        select_from(User).\
        join(Document, User.email == Document.author).\
        filter(User.email == 'someemail').all()