Foreign key

As explained in Django in Action

A foreign key relationship is a database relationship in which records in one table reference a record in another table through a foreign key.

A foreign key connects a row in one database table to a row in another by storing the related row’s ID. In Django, a ForeignKey model field creates that relationship column. section 4.7 section 4.7.2

Use the relationship shape to choose the database design:

• One-to-many: one venue can have multiple rooms, while each room belongs to one venue. section 4.7
• Many-to-many: use a separate relationship table containing foreign keys to both participating tables, rather than one ForeignKey column. section 4.7 section 4.7.2
• Django provides ForeignKey for one-way relationships and ManyToManyField for relationships that work in both directions. section 4.7 section 4.7.2

Rooms belonging to venues

Model a venue-to-room relationship with a ForeignKey on Room. The database stores the venue ID on each room row, allowing several rooms to reference one venue while keeping each room associated with a single venue. section 4.7

Figure 4.9 One-to-many vs. many-to-many relationships

Compare one-to-many foreign-key relationships with many-to-many relationships before choosing a Django model field. section 4.7

How Django in Action covers it

How deep it goes

Defines stored IDs and contrasts one-to-many with relationship-table many-to-many designs, without detailing migrations or query code.

Examples

Uses venues and rooms for one-to-many relationships, and musicians and bands for many-to-many relationships.

What it assumes

Defines database tables and related-row IDs while introducing relationship cardinality through concrete venue, room, musician, and band examples.

What you can do after

Apply it via Django ORM by distinguishing ForeignKey columns from ManyToManyField relationship tables.

How it connects

Connects database tables, record IDs, one-to-many relationships, many-to-many relationships, ForeignKey, and ManyToManyField.

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  The Well-Grounded Python Developer: How the pros use Python and FlaskA foreign key is a column or set of columns that references a primary key in another relational database table to establish a relationship.
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  DuckDB in ActionA foreign key is a schema constraint requiring values in one table to reference corresponding values in another table.
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  Build Python Web Apps with StreamlitA foreign key constraint requires values in one table's column to correspond to existing values in a referenced table's key column.
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  100 SQL Server Mistakes and How to Avoid ThemA foreign key is a column or set of columns whose values reference a candidate key in another or the same table.
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  Just Use Postgres!A foreign key constraint requires values in a column or set of columns to match existing unique or primary-key values in a referenced table.
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  AI-Powered SearchA foreign key is a value or column in one table that references an entity or key in another table to link records.
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  Rust Servers, Services, and AppsA foreign-key constraint is a database rule requiring values in one table's column to reference valid values in another table's key column.
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  Effective Data AnalysisA foreign key is a column or set of columns whose values reference a key in another table to represent a relationship between rows.
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  Kafka Streams in Action, Second EditionA foreign key is a field whose value references a key in another table or record set.
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  PostgreSQL Mistakes and How to Avoid ThemA foreign key relationship is a referential association in which columns in one table identify rows in another input table.
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  .NET in Action, Second EditionA foreign key is a relational-database column or set of columns whose values reference a key in another table.
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  Unit Testing Principles, Practices, and PatternsA foreign key constraint requires values in one database column or set of columns to correspond to valid values in another table.

Compare how 18 books explain foreign key →

Related concepts

• primary keyuses · A primary key is a designated column or attribute, or combination of them, that uniquely identifies each row or item in a table or data store.
• constraintkind of · A constraint is a condition or rule that restricts the permissible states, values, actions, or solutions in a system or problem.
• on delete cascadeconfigured by · ON DELETE CASCADE is a relational foreign-key action that automatically deletes referencing rows when their referenced row is deleted.
• referential integrityimplements · Referential integrity is the database property that references between related records correspond to valid existing keys or records.
• joinused by · A join is an operation that combines records or rows from multiple data sources according to specified matching conditions or relationships.
• schemapart of · A data schema is a formal specification of the structure, fields, types, relationships, and constraints of data.

This explainer was generated by Manning's knowledge graph from the text of Django in Action. The section links point to the parts of the book it draws on.