foreign-keys

问题 I'm following the flask-sqlalchemy tutorial on declaring models regarding one-to-many relationship. The example code is as follows: class Person(db.Model): id = db.Column(db.Integer, primary_key=True) name = db.Column(db.String(50)) addresses = db.relationship('Address', backref='person', lazy='dynamic') class Address(db.Model): id = db.Column(db.Integer, primary_key=True) email = db.Column(db.String(50)) person_id = db.Column(db.Integer, db.ForeignKey('person.id')) Now I'm wondering how to

问题 Closed . This question needs details or clarity. It is not currently accepting answers. Want to improve this question? Add details and clarify the problem by editing this post. Closed 5 days ago . Improve this question I have Types column in my Help Table and I want to add foreign key to the Id column in my HelpType table but not really sure what I'm doing wrong so. If I can get any suggestion or help will be really appreciated. ALTER TABLE Help ADD CONSTRAINT FK_Types FOREIGN KEY (Types)

问题 I'm importing a CSV file of ~150k rows into a MySQL (InnoDB) table. At some point during the import, there's a failure because of a foreign key constraint error. It shows which column the failure is occuring on: Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails (`db`.`table`, CONSTRAINT `fk` FOREIGN KEY (`otherTableId`) REFERENCES `otherTable` (`otherTableId`)) Is it possible to "catch" what that value is? I haven't tried anything yet, because I don't know

问题 I'm importing a CSV file of ~150k rows into a MySQL (InnoDB) table. At some point during the import, there's a failure because of a foreign key constraint error. It shows which column the failure is occuring on: Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails (`db`.`table`, CONSTRAINT `fk` FOREIGN KEY (`otherTableId`) REFERENCES `otherTable` (`otherTableId`)) Is it possible to "catch" what that value is? I haven't tried anything yet, because I don't know

问题 I'm importing a CSV file of ~150k rows into a MySQL (InnoDB) table. At some point during the import, there's a failure because of a foreign key constraint error. It shows which column the failure is occuring on: Error Code: 1452. Cannot add or update a child row: a foreign key constraint fails (`db`.`table`, CONSTRAINT `fk` FOREIGN KEY (`otherTableId`) REFERENCES `otherTable` (`otherTableId`)) Is it possible to "catch" what that value is? I haven't tried anything yet, because I don't know

问题 public class A { [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public virtual int Aid { get; set; } public virtual ICollection<B> B { get; set; } } public class B { [DatabaseGenerated(DatabaseGeneratedOption.Identity)] public virtual int Bid { get; set; } [Key] [Column(Order = 0)] [Required] Public virtual string BName {get ; set} [Key] [Column(Order = 1)] [Required] public virtual int Aid { get; set; } [ForeignKey("Aid")] public virtual A A { get; set; } public virtual ICollection<C>

问题 I need to change the type of a field in one of my Django models from CharField to ForeignKey . The fields are already populated with data, so I was wondering what is the best or right way to do this. Can I just update the field type and migrate, or are there any possible 'gotchas' to be aware of? N.B : I just use vanilla Django management operations ( makemigrations and migrate ), not South. 回答1: This is likely a case where you want to do a multi-stage migration. My recommendation for this

问题 I have imported some data to a temp SQL table from an Excel file. Then I have tried to insert all rows to two related tables. Simply like this: There are Events and Actors tables with many to many relationship in my database. Actors are already added. I want to add all events to Events table and then add relation(ActorId) for each event to EventActors tables. (dbo.TempTable has Title, ActorId columns) insert into dbo.Event (Title) Select Title From dbo.TempTable insert into dbo.EventActor

问题 I have a hierarchical entity, which references it self as a parent. I need to do the mapping only via ids, not via entity instances (the reason is too complicated to explain). So I defined the entity this way: class Item { @Id private String id; @ManyToOne(targetEntity = Item.class) @JoinColumn(name = "PARENT_ID", nullable = true) private String parentId; } This seems to work fine. The foreign key constraint is created correctly in database. But when I execute the following query: SELECT i

问题 I have a hierarchical entity, which references it self as a parent. I need to do the mapping only via ids, not via entity instances (the reason is too complicated to explain). So I defined the entity this way: class Item { @Id private String id; @ManyToOne(targetEntity = Item.class) @JoinColumn(name = "PARENT_ID", nullable = true) private String parentId; } This seems to work fine. The foreign key constraint is created correctly in database. But when I execute the following query: SELECT i