Typically, the parent key is the primary key of the parent table. The group_id column in the supplier_groups table is called the parent key, which is a column or a set of columns in the parent table that the foreign key constraint references. The suppliers table is known as a child table, which is the table to which the foreign key constraint applies. The supplier_groups table is called a parent table, which is the table that a foreign key references. To add the foreign key constraint to the suppliers table, you change the definition of the CREATE TABLE statement above as follows: DROP TABLE suppliers Ĭode language: SQL (Structured Query Language) ( sql ) To enforce the relationship between rows in the suppliers and supplier_groups table, you use the foreign key constraints. This may leave orphaned rows in the suppliers table. In addition, you may remove a row in the supplier_groups table without deleting or updating the corresponding rows in the suppliers table. In other words, for each row in the suppliers table, there is a corresponding row in the supplier_groups table.Ĭurrently, there is no way to prevent you from adding a row to the suppliers table without a corresponding row in the supplier_groups table. The relationship between supplier_groups and suppliers tables is one-to-many. And each supplier group may have zero or many suppliers. ) Code language: SQL (Structured Query Language) ( sql )Īssuming that each supplier belongs to one and only one supplier group. Let’s start with two tables: suppliers and supplier_groups : CREATE TABLE suppliers ( To enable foreign key constraint: PRAGMA foreign_keys = ON Code language: SQL (Structured Query Language) ( sql ) Introduction to the SQLite foreign key constraints To disable foreign key constraint: PRAGMA foreign_keys = OFF Code language: SQL (Structured Query Language) ( sql ) If the SQLite library is compiled with foreign key constraint support, the application can use the PRAGMA foreign_keys command to enable or disable foreign key constraints at runtime. If the command returns nothing, it means that your SQLite version doesn’t support foreign key constraints. The command returns an integer value: 1: enable, 0: disabled. ![]() ![]() PRAGMA foreign_keys Code language: SQL (Structured Query Language) ( sql ) To check whether your current version of SQLite supports foreign key constraints or not, you use the following command. The SQLite library must also be compiled with neither SQLITE_OMIT_FOREIGN_KEY nor SQLITE_OMIT_TRIGGER. SQLite has supported foreign key constraint since version 3.6.19. To enable foreign key constraints on a connection you created yourself with open,Įxecute the SQL command PRAGMA foreign_keys=on with it.Summary: in this tutorial, you will learn how to use the SQLite foreign key constraint to enforce the relationships between related tables. Sqlite does not enable checking for foreign key constraintsīut Norm does so automatically for every connection that Norm creates. Please note that Sqlite enforces foreign key constraints only when you use getDb() Select queries will only return the id referenced and not the associated fields: var consumer = newConsumer()ĭb.select(consumer, "email = $1", = product = newProduct()ĭb.select(product, "id = $1", consumer.productId)Įcho() SELECT "Consumer".email, "Consumer".productId, "Consumer".id FROM "Consumer" WHERE email = $1 LIMIT 1 <- "Product".name, "Product".price, "Product".id FROM "Product" WHERE id = $1 LIMIT 1 <. Let badProductId = 133 var paul = newConsumer( badProductId)Įcho getCurrentExceptionMsg() INSERT INTO "Consumer" (email, productId) VALUES(?, ?) <- 133] If an invalid ID is passed, Norm will raise a DbError exception: try: ![]() ![]() INSERT INTO "Consumer" (email, productId) VALUES(?, ?) <- 1] This allows for more flexibility at the cost of more manual queries: var cheese = Product(name: "Cheese", price: 13.30)Įcho() INSERT INTO "Product" (name, price) VALUES(?, ?) <- 13.3] INSERT statements can now be done using only id. When using fk pragma, foreign key must be handled manually, so createTables needs to be called for both Models: let db = open( ":memory:", "", "", "")Įcho() CREATE TABLE IF NOT EXISTS "Product"(name TEXT NOT NULL, price FLOAT NOT NULL, id INTEGER NOT NULL PRIMARY KEY)ĬREATE TABLE IF NOT EXISTS "Consumer"(email TEXT NOT NULL, productId INTEGER NOT NULL, id INTEGER NOT NULL PRIMARY KEY, FOREIGN KEY (productId) REFERENCES "Product"(id)) Proc newConsumer(email = "", productId = 0'i64): Consumer =Ĭonsumer(email: email, productId: productId) ProductId : int64 proc newProduct(): Product = Price: float Consumer = ref object of Model To work around that limitation, you can declare and handle foreign keys manually, with fk pragma: import norm/ However, it has a downside: to fill up an object from the DB, Norm always fetches all related objects along with the original one, potentially generating a heavy JOIN query. Norm handles foreign keys automatically if you have a field of type Model.
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