One-to-one relationship
A one-to-one relationship is an association in which each instance of either entity type relates to at most one instance of the other type.
Grokking Relational Database Design
A one-to-one relationship is a relationship in which each entity instance is associated with at most one instance of the other entity in both directions.
- How it is used
- Uses maximum cardinality to model entity pairs where neither side connects to more than one instance.
- How deep it goes
- Explains maximum and minimum cardinalities, notation, foreign-key placement, and insertion constraints.
- Examples
- Uses department-manager and dealer-address relationships to illustrate one-to-one associations.
- What you can do after
- Apply it to choose cardinalities, place a foreign key, and adjust optionality for workable data entry.
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Java Persistence with Spring Data and Hibernate epub
A one-to-one association is an association in which each entity instance is related to at most one instance of the other entity type.
- How it is used
- Models exclusive associations between entity instances when each side may reference at most one instance of the other.
- How deep it goes
- Compares component, shared-primary-key, foreign-key, and join-table mappings, including schema constraints and lazy-loading behavior.
- Examples
- Uses User–Address mappings, an optional Shipment–Item link, SQL schemas, repository interfaces, annotations, and persistence tests.
- What you can do after
- Apply it via JPA annotations or Spring Data JDBC mappings while selecting storage based on lifecycle, identity, and optionality.
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Django in Action
A one-to-one relationship is a relationship in which each record on one side corresponds to at most one record on the other side.
- How it is used
- Separates extra user data from account data while preserving one profile per user.
- How deep it goes
- Implements the model field, deletion behavior, admin integration, and migration workflow without exploring database internals.
- Examples
- Uses RiffMates UserProfile, musician profiles, controlled venues, stacked inlines, and the Django Admin user screen.
- What you can do after
- Apply it via Django ORM and Django Admin to attach one profile model to each user account.
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Related concepts
- @OneToOneconfigured by · @OneToOne is a Jakarta Persistence annotation that declares an entity-valued property as a one-to-one association.
- foreign keyuses · A foreign key is a column or set of columns in a relational table whose values reference a candidate key in the same or another table, establishing a relationship and supporting referential integrity.
- shared primary key valueincludes · A shared primary key value is a one-to-one mapping strategy in which associated entities use the same database primary-key value.
- minimum cardinalityconfigured by · Minimum cardinality is the smallest number of related entity instances required or permitted for an entity instance in a relationship.
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