How to Efficiently Join Multiple Tables in SQLAlchemy with a Single Query?

Joining Multiple Tables in SQLAlchemy Using One Query

SQLAlchemy allows for efficient data retrieval by joining multiple tables with a single query. To join several tables, it requires you to define relationships between the classes representing the tables in your database.

In your case, you have three classes: User, Document, and DocumentsPermissions. Let's establish relationships between these classes:

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"), nullable=False)

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

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

With these relationships, you can retrieve the desired table using a single query:

query = session.query(User, Document, DocumentsPermissions) \
    .filter(User.email == Document.author) \
    .filter(Document.name == DocumentsPermissions.document) \
    .filter(User.email == "[email protected]") \
    .all()

This query joins User, Document, and DocumentsPermissions tables by their relationships and filters the results based on email. The final result will be a list of tuples containing data from all three tables, as you described. By using this method, you can efficiently retrieve data from multiple tables with a single database query.

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