Skip to main content

Relationships

Relationships define how tables connect to each other via foreign keys.

Cardinality types​

One-to-many (most common)​

One row in table A relates to many rows in table B.

Example: One supplier has many products

"Add a supplier_id foreign key to products that references suppliers.id"

One-to-one​

One row in table A relates to exactly one row in table B.

Example: One purchase_order has one shipment

"Create a one-to-one relationship between purchase_orders and shipments via purchase_order_id"

Many-to-many​

Many rows in table A relate to many rows in table B, via a junction table.

Example: products and warehouses (a product can be stocked in many warehouses, a warehouse holds many products)

"Create a many-to-many relationship between products and warehouses using an inventory junction table with quantity_on_hand"

Defining relationships via chat​

The AI understands natural language relationship descriptions:

  • "Products belong to one supplier"
  • "Purchase orders have many line items"
  • "A product can be stocked in many warehouses, and each warehouse holds many products"
  • "Add a self-referential relationship to the warehouses table for parent_warehouse_id"

ERD relationship visualization​

In the ERD canvas:

  • Lines connect related tables
  • Crow's foot notation shows cardinality (one side vs. many side)
  • FK badge marks foreign key fields in the table node

Foreign key constraints​

TalkingSchema generates proper FOREIGN KEY constraints in exported SQL, including ON DELETE and ON UPDATE behavior.

Specify cascade behavior via chat:

"Set ON DELETE CASCADE on purchase_order_items.po_id so deleting a purchase order removes all its line items"

Junction tables (many-to-many)​

For many-to-many relationships, TalkingSchema creates a junction table automatically:

CREATE TABLE inventory (
  warehouse_id UUID NOT NULL REFERENCES warehouses(warehouse_id) ON DELETE CASCADE,
  product_id   UUID NOT NULL REFERENCES products(product_id) ON DELETE CASCADE,
  quantity_on_hand INTEGER NOT NULL DEFAULT 0,
  reorder_point    INTEGER NOT NULL DEFAULT 0,
  PRIMARY KEY (warehouse_id, product_id)
);

You can add extra fields to junction tables:

"Add a last_counted_at timestamp to the inventory table"