Sqlite foreign key cascade example code#
Sqlite foreign key cascade example windows#

In the Database tool window ( View | Tool Windows | Database), expand the data source tree until the node of a child table. In the following example, activity.activity_id is a primary key, while visitor.activity_id is a foreign key.

If your database contains explicit foreign key relationships, IntelliJ IDEA automatically uses them in auto-completion, data navigation, and diagrams. The table that contains a candidate key is a referenced or target table. The table that contains a foreign key is a child table. If the table contains data that you want to keep, you can transfer that data to another table, before transferring it back once you’ve created the new table with the foreign key constraint.FOREIGN KEY (activity_id) REFERENCES activity(activity_id) Therefore, if you need to add a foreign key to an existing table, you’ll need to drop the table and create it again with the foreign key constraint. The ALTER TABLE statement in SQLite is very limited, and it doesn’t allow for adding a foreign key to an existing table. Adding a Foreign Key to an Existing Table As mentioned, you’ll need to enable foreign key support before your foreign keys will be enforced. If you don’t get this error, and the data was successfully inserted, you haven’t enabled foreign key support.

It therefore, helped us maintain data integrity. So our foreign key successfully prevented bad data from entering the database. Result: Error: FOREIGN KEY constraint failed a TypeId value that doesn’t exist in the Types column). Let’s try to add a pet that uses a non-existent TypeID (i.e. sqlite> SELECT * FROM Pets īut now let’s try inserting data that violates the foreign key. The tables now contain the data shown above. Now that our tables have been created with the appropriate foreign key, we can add data. In this case it will reference the TypeId column of the Types table. The REFERENCES Types(TypeId) specifies the column that our foreign key will reference. The FOREIGN KEY(TypeId) part declares Pets.TypeId as the foreign key.Īlthough I didn’t qualify the column name with its table name, we know it’s Pets.TypeId (and not Types.TypeId) because we’re running this in the CREATE TABLE statement for Pets. The part that creates the foreign key is this: FOREIGN KEY(TypeId) REFERENCES Types(TypeId) CREATE TABLE Types(įOREIGN KEY(TypeId) REFERENCES Types(TypeId)

Sqlite foreign key cascade example code#

We can use the following code to create these two tables. In this example we’ll make it the primary key. While parent keys are usually also the primary key for the table, this is not actually a requirement. In other words, we want to make Pets.TypeId the child key (with a foreign key constraint), and Types.TypeId the parent key (with a primary key constraint). Imagine we want two tables with the following data.Īnd we want the TypeId column of the Pets table to reference the TypeId column of the Types table. Now that we’ve enabled foreign key support, let’s go ahead and create a foreign key. Note that this setting is not required for creating foreign keys, but it is required for enforcing foreign keys. If you open another connection, you’ll need to run the same statement for that connection. This will enable foreign key enforcement for your database connection. To do this, run the following statement: PRAGMA foreign_keys = ON The first thing we should do is to enable foreign key support (if it hasn’t already been done).Īssuming your SQLite library hasn’t been compiled with SQLITE_OMIT_FOREIGN_KEY or SQLITE_OMIT_TRIGGER defined, you will still need to enable foreign key support at runtime. This article provides an example of creating a foreign key when creating a table in SQLite.

When you create a table in SQLite, you can also create a foreign key in order to establish a relationship with another table.