Since Table2 has a composite primary key (FileID, FileType), then any reference to it must also include both columns. ALTER TABLE dbo.Table1 ADD CONSTRAINT FK_Table1_Table2 FOREIGN KEY(FileID, FileType) REFERENCES Table2(FileID, FileType) Unless you have a unique constraint/index on the Table2.FileID field (but if so: why isn’t this the PK??), you cannot create a FK relationship … Read more
It means that the primary key in tblOne hasn’t been properly declared – you need to go to tblOne and add the PRIMARY KEY constraint back onto it. If you’re sure that tblOne does have a PRIMARY KEY constraint, then maybe there are multiple tblOne tables in your DB, belonging to different schemas, and your … Read more
A foreign key must reference only one parent table. This is fundamental to both SQL syntax, and relational theory. A Polymorphic Association is when a given column may reference either of two or more parent tables. There’s no way you can declare that constraint in SQL. The Polymorphic Associations design breaks rules of relational database … Read more
Well, there’s essentially two questions here: What is the difference (in general) between one to one, many to many, and foreign key relations What are their differences specific to Django. Both of these questions are quite easily answered through a simple Google search, but as I cannot find an exact dupe of this question on … Read more
Old question but adding answer so that one can get help Its two step process: Suppose, a table1 has a foreign key with column name fk_table2_id, with constraint name fk_name and table2 is referred table with key t2 (something like below in my diagram). table1 [ fk_table2_id ] –> table2 [t2] First step, DROP old … Read more
Error indicates that there is no UserID column in your Employees table. Try adding the column first and then re-run the statement. ALTER TABLE Employees ADD CONSTRAINT FK_ActiveDirectories_UserID FOREIGN KEY (UserID) REFERENCES ActiveDirectories(id);
You must make your foreign key nullable: public class User { public int Id { get; set; } public int? CountryId { get; set; } public virtual Country Country { get; set; } }
In one-to-one relation one end must be principal and second end must be dependent. Principal end is the one which will be inserted first and which can exist without the dependent one. Dependent end is the one which must be inserted after the principal because it has foreign key to the principal. In case of … Read more