What is related_name used for?

The related_name attribute specifies the name of the reverse relation from the User model back to your model. If you don’t specify a related_name, Django automatically creates one using the name of your model with the suffix _set, for instance User.map_set.all(). If you do specify, e.g. related_name=maps on the User model, User.map_set will still work, but the User.maps. syntax is obviously a bit cleaner and less clunky; so for example, if you …

Read more

MySQL Error 1215: Cannot add foreign key constraint

I’m guessing that Clients.Case_Number and/or Staff.Emp_ID are not exactly the same data type as Clients_has_Staff.Clients_Case_Number and Clients_has_Staff.Staff_Emp_ID. Perhaps the columns in the parent tables are INT UNSIGNED? They need to be exactly the same data type in both tables.

entity object cannot be referenced by multiple instances of IEntityChangeTracker. while adding related objects to entity in Entity Framework 4.1

Because these two lines … … don’t take a parameter in the constructor, I guess that you create a context within the classes. When you load the city1… …you attach the city1 to the context in CityService. Later you add a city1 as a reference to the new Employee e1 and add e1 including this reference to city1 to the context in EmployeeService. As a result you have city1 attached to …

Read more

sqlite3 “foreign key constraint failed”

I’ve set up two tables: After I insert data into A, it looks like this: After I insert data into B, it looks like this: I then execute the following statement: I get the following: “Error: foreign key constraint failed” I then restart sqlite3 and try again but this time I enter this first: it …

Read more