Flask-SqlAlchemy關系錯誤

Question

這是我有的簡單模型

  class Record(db.Model):
      __tablename__ = 'reg_records'
      request_id = db.Column(db.Integer, primary_key = True)
      title = db.Column(NVARCHAR())

  class Field(db.Model):
      __tablename__ = 'reg_fields'
      request_id = db.Column(db.Integer, primary_key= True) 
      name = db.Column(NVARCHAR(), primary_key = True)

現在，我想映射相關的字段進行記錄。 我正在遵循flask-sqlalchemy規格並獲取此

  class Field(db.Model):
      __tablename__ = 'reg_fields'
      request_id = db.Column(db.Integer, ForeignKey('record.request_id'), primary_key= True) 
      name = db.Column(NVARCHAR(), primary_key = True)

  class Record(db.Model):
      __tablename__ = 'reg_records'
      request_id = db.Column(db.Integer, primary_key = True)
      title = db.Column(NVARCHAR())
      fields = db.relationship(Field, backref = 'record')

但是，當我嘗試使用此模型時，出現以下錯誤

  sqlalchemy.exc.NoForeignKeysError
  NoForeignKeysError: Could not determine join condition between parent/child tables on relationship Record.fields - there are no foreign keys linking these tables.  Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.

將primaryjoin添加到關系聲明中，如下所示

    fields = db.relationship(Field, backref = 'record', primaryjoin='Record.request_id==Field.request_id')

無法解決問題，而是給出了新的例外

    sqlalchemy.exc.NoReferencedTableError
    NoReferencedTableError: Foreign key associated with column 'reg_fields.request_id' could not find table 'record' with which to generate a foreign key to target column 'request_id'

如果我將類名替換為primaryjoin值中的表名，

    fields = db.relationship(Field, backref = 'record', primaryjoin='reg_records.request_id==reg_fields.request_id')

我又遇到另一個例外

   sqlalchemy.exc.InvalidRequestError
   InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers.  Original exception was: 'Table' object has no attribute 'request_id' 

總體而言，在flask-sqlalchemy中建立一對多關系的正確方法是什么。

Answer 1

目前尚不清楚您要做什么。 我假設您正在嘗試在記錄和字段之間建立一對多關系（一個記錄可以有零個或多個字段）。 我還假設您希望每個記錄僅具有一個名為name的字段。 我認為您希望使用以下模型來設置表和關系：

from sqlalchemy.schema import UniqueConstraint

class Record(db.Model):
    __tablename__ = 'reg_records'

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(NVARCHAR())


class Field(db.Model):
    __tablename__ = 'reg_fields'
    __table_args__ = (
        UniqueConstraint('record_id', 'name', name='record_id_name_uix'),
    )

    id = db.Column(db.Integer, primary_key=True)
    record_id = db.Column(db.Integer, ForeignKey(Record.id))
    name = db.Column(NVARCHAR())

    record = db.relationship(Record, backref='fields')

現在，您可以執行諸如創建新的記錄和字段的操作：

record = Record(title='a record')
record.fields.append(Field(name='field1'))
record.fields.append(Field(name='field2'))
db.session.add(record)
db.session.commit()

但是，嘗試為同一條記錄創建兩個具有相同名稱的字段，嘗試提交它們時會收到IntegrityError：

record = Record(title='another record')
record.fields.append(Field(name='same_name'))
record.fields.append(Field(name='same_name'))
db.session.add(record)
db.session.commit()

最后，請嘗試更加謹慎地設置Python代碼的格式，很難理解。