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What is a relationship in EF Core?
A relationship describes how two entity types are associated. EF Core represents relationships using primary keys, foreign keys, and navigation properties.
Entity Framework Core Interview
Relationships, Navigation Properties & Loading Data
Entity Framework Core interview questions covering relationships, navigation properties, foreign keys, eager loading, explicit loading, lazy loading and related data.
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What is a navigation property in EF Core?
A navigation property represents a relationship between entities in the object model. A reference navigation points to one related entity, while a collection navigation points to multiple related entities.
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What is a foreign key property in EF Core?
A foreign key property stores the key value that links a dependent entity to its principal entity. EF Core can often discover foreign keys by conventions such as CustomerId for a Customer navigation.
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What is a one-to-many relationship in EF Core?
A one-to-many relationship means one principal entity can be associated with many dependent entities, while each dependent is associated with one principal.
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What is a one-to-one relationship in EF Core?
A one-to-one relationship means one entity is associated with at most one related entity on the other side.
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What is a many-to-many relationship in EF Core?
A many-to-many relationship means each entity on either side can relate to multiple entities on the other side. For example, a Student can take many Courses and a Course can have many Students.
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When should you use an explicit join entity for a many-to-many relationship?
Use an explicit join entity when the relationship has its own data or behavior. Examples include enrollment date between Student and Course, quantity between Order and Product, or assigned role between User and Project.
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What are principal and dependent entities in EF Core relationships?
The principal entity is the entity whose key is referenced by the relationship. The dependent entity contains the foreign key that points to the principal.
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What is a required relationship in EF Core?
A required relationship means the dependent must be associated with a principal. For a relational database, the foreign-key column is normally non-nullable.
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What is an optional relationship in EF Core?
An optional relationship allows the dependent entity to exist without an associated principal. The foreign-key property is normally nullable.
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How do you configure relationships with the Fluent API?
Relationship configuration typically starts with HasOne or HasMany and continues with WithOne or WithMany. HasForeignKey can explicitly identify the dependent foreign-key property.
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What is relationship fix-up in EF Core?
Relationship fix-up is EF Core's process of keeping navigation properties and foreign-key values synchronized for tracked entities.
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What is eager loading in EF Core?
Eager loading retrieves related data as part of the query by using Include and ThenInclude.
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What are Include and ThenInclude?
Include specifies a related navigation to load with the main query. ThenInclude continues from an included navigation to load another level of related data.
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What is explicit loading in EF Core?
Explicit loading loads related data for an entity after that entity has already been queried and is being tracked.
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What is lazy loading in EF Core?
Lazy loading retrieves related data automatically when a navigation property is accessed. EF Core can support lazy loading through proxies or other configured mechanisms.
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What is the N+1 query problem?
The N+1 problem occurs when one query loads a set of parent records and then an additional query is executed for each parent to load related data.
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What is projection in EF Core?
Projection uses Select to retrieve only the columns and related values needed by the application instead of materializing complete entity graphs.
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What is a split query in EF Core?
A split query loads certain included collection relationships using multiple SQL queries instead of one large joined query.
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What is a single query in EF Core?
A single query retrieves an included entity graph through one SQL query, typically using joins. This avoids the multiple round trips associated with split queries.
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What is cascade delete in EF Core?
Cascade delete means deleting a principal can automatically cause related dependent rows to be deleted when the relationship and database behavior are configured for cascading.
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What is DeleteBehavior in EF Core?
DeleteBehavior controls how EF Core and the database handle a relationship when a principal entity is deleted or a relationship is severed.
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What are shadow properties in EF Core?
A shadow property exists in the EF Core model but not as a CLR property on the entity class. EF Core stores its value in the change tracker.
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What is a self-referencing relationship in EF Core?
A self-referencing relationship occurs when an entity type relates to another entity of the same type.
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What are best practices for relationships and loading related data in EF Core?
Model relationships according to real business rules and make principal/dependent roles, requiredness, foreign keys, and delete behavior clear. Use explicit Fluent API configuration where conventions are ambiguous.