foreign-keys

来源： https://stackoverflow.com/questions/63508302/showing-foreign-key-relationship-in-model-class-using-icollection

来源： https://stackoverflow.com/questions/63862777/foreign-key-to-one-to-all-relationship

来源： https://stackoverflow.com/questions/63862777/foreign-key-to-one-to-all-relationship

问题 I'm creating a table, but I get this error: number of referencing and referenced columns for foreign key disagree. I don't know how to solve it. I think that it may be a problem with declaring 3 foreign keys, but, I'm not sure about it. What is the problem? Create table Trasllat ( Data Date, Codi_Empleat Integer, Nom_agencia Varchar(30), Data_fi Date, Primary key (Data, Codi_Empleat), Foreign key (Data) references Data on delete cascade, Foreign key (Codi_empleat) references Empleat on delete

问题 I'm creating a table, but I get this error: number of referencing and referenced columns for foreign key disagree. I don't know how to solve it. I think that it may be a problem with declaring 3 foreign keys, but, I'm not sure about it. What is the problem? Create table Trasllat ( Data Date, Codi_Empleat Integer, Nom_agencia Varchar(30), Data_fi Date, Primary key (Data, Codi_Empleat), Foreign key (Data) references Data on delete cascade, Foreign key (Codi_empleat) references Empleat on delete

问题 I'm trying to build an example with several related models, like the following. We have a model B with a 1:n relation with a model C; then we have a model A with a n:1 relation with B and a n:1 relation with C. (C has a 2-columns primary key) I tried this code: class C(db.Model): __tablename__ = 'C' key1 = Column(Integer, primary_key=True) key2 = Column(Integer, primary_key=True) attr1 = Column(Date) attr2 = Column(Boolean) related_b = Column(Integer, ForeignKey('B.spam')) class B(db.Model):

问题 I have a Pandas DataFrame that has a column that is basically a foreign key, as below: Index | f_key | values 0 | 1 | red 1 | 2 | blue 2 | 1 | green 3 | 2 | yellow 4 | 3 | orange 5 | 1 | violet What I would like is to add a column that labels the repeated foreign keys sequentially, as in "dup_number" below: Index | dup_number | f_key | values 0 | 1 | 1 | red 1 | 1 | 2 | blue 2 | 2 | 1 | green 3 | 2 | 2 | yellow 4 | 1 | 3 | orange 5 | 3 | 1 | violet The rows can be reordered if needed, I just

问题 I'm using Entity Framework Core with Code First approach but recieve following error when updating the database: Introducing FOREIGN KEY constraint 'FK_AnEventUsers_Users_UserId' on table 'AnEventUsers' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint or index. See previous errors. My entities are these: public class AnEvent { public int AnEventId { get; set; } public DateTime

问题 This question was originally asked by @PrateekGupta Background @PrateekGupta wanted to perform bulk insert operation on multiple tables. The tables have foreign key relationships between themselves. If an INSERT operation is done on a table with a foreign key before the referenced table is being inserted to, the operation might fail due to violation of the foreign key. Requirement Produce a list of tables within a database ordered according to their dependencies. Tables with no dependencies

问题 Address ( addressID , houseNumber, postcode, roadName, city, county) Reservation ( reservationID , roomNo, leadGuestID, guest2ID, guest3ID , arrivalDate, departureDate, addressID , amountOutstanding) Guest ( guestID , firstName, lastName, adultFlag, telephoneNo, addressID , emailAddress) Room ( roomNo , roomTypeName ) RoomType ( roomTypeName , floor, basePrice, extraAdultPrice, extraChildPrice) The above schema is supposed to be normalised 4NF. But I cannot see how leadGuestID, guest2ID &