Avoid adding a repository by default when it only forwards generic CRUD calls to an ORM such as EF Core. An extra layer is useful when it creates a meaningful domain or persistence boundary, consolidates important query logic, or supports a deliberate testing strategy—not simply because repositories are a familiar pattern.
What the Repository pattern is meant to do
Martin Fowler defines a Repository as an intermediary between the domain and data-mapping layers that provides a collection-like way to access domain objects. The pattern can give query construction and mapping a home, reduce duplicated query logic, and separate domain code from persistence details. Fowler describes it as a stronger fit for complex domain models, many domain classes, or heavy querying. See Fowler’s Repository catalog entry and Patterns of Enterprise Application Architecture.
That purpose is narrower than wrapping every ORM method in a matching repository method. If an interface simply repeats generic create, read, update, and delete operations, it may add indirection without adding a useful boundary.
Why I often avoid adding one by default
EF Core already supplies similar building blocks
Microsoft’s .NET architecture guidance notes that EF Core’s DbContext provides repository- and unit-of-work-like behavior in its sample architecture. The same guidance says repositories can be useful but are not essential to domain-driven design. An additional layer therefore needs a concrete job beyond reproducing what the context already does. See Microsoft’s persistence-layer guidance.
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Testability alone may not justify a repository for every query
A repository can let an application test substitute query results, but it also means designing and maintaining methods for the queries callers need. Microsoft’s EF Core testing guidance calls out that cost and notes that tests against the real database may still be necessary. See EF Core testing guidance.
There is also a boundary trade-off: a repository that exposes IQueryable lets callers continue composing provider-backed LINQ queries, so it does not hide much about the query provider. In Microsoft’s described test-double approach, query results are stubbed directly and the repository returns IEnumerable; the guidance cautions that IQueryable methods cannot be stubbed in the same way. This is a choice for that testing objective, not a universal rule for repository APIs.
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A hypothetical database migration is weak justification
An abstraction is not valuable merely because a different database might be chosen someday. Fowler’s discussion of dependency inversion emphasizes placing abstractions at a level that suits the domain: a useful repository translates domain-sensible requests into database-sensible ones. A real persistence boundary or a requirement for different implementations is stronger justification than speculative replacement. See Fowler on dependency inversion.
When a repository earns its cost
- It expresses domain operations. The interface speaks in terms meaningful to the application rather than mirroring an ORM’s generic API.
- It centralizes duplicated or complex queries. Shared query logic has one maintained home instead of being repeated across callers.
- It isolates a real persistence boundary. The domain or application needs separation from infrastructure, or the system genuinely supports different persistence implementations.
- It supports a deliberate unit-testing seam. Application logic can be tested with supplied query outputs without executing LINQ.
These are trade-offs, not a universal case against repositories. The key question is whether the interface concentrates meaningful behavior or merely adds another layer to maintain.
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Choose the approach by the job you need done
| Approach | Best suited to | Important limitation |
|---|---|---|
| Use EF Core directly | Applications where DbContext already provides the needed persistence operations and another boundary would repeat its API. |
Domain or application code remains coupled to EF Core unless another boundary is introduced. |
| Add a focused repository | Meaningful domain-facing persistence operations, shared complex queries, a real persistence boundary, or application tests that need substituted query outputs. | Methods and implementations add design and maintenance work; exposing IQueryable may leave query-provider behavior visible. |
| Test against the database | Verifying that important queries behave correctly with the actual database provider. | These tests execute against a database rather than replacing it with a query-output stub. |
The approaches can coexist: a focused repository may support application unit tests, while integration tests exercise critical queries against the production database provider.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Keep real-provider coverage for important queries
A stubbed repository can test application logic that consumes query results; it does not prove that the LINQ works as intended on the production database. Fake providers and in-memory evaluation can differ from a real provider, including in case sensitivity and support for provider-specific methods. Microsoft documents these limitations in its EF Core testing guidance. Keep database integration tests for queries whose provider behavior matters.
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A practical decision checklist
- Name the boundary. Write down what the repository separates or what domain operation it expresses. If the answer is only “it wraps EF Core,” reconsider it.
- Check query concentration. Identify duplicated or complex queries that would benefit from a shared home; avoid creating methods solely to mirror each ORM call.
- Define the test goal. Use a test double when the goal is to supply results to application logic. Use database integration coverage when the goal is to verify provider behavior.
- Count the ongoing cost. Consider the repository methods, implementations, and upkeep the design adds, especially if queries change often.
- Confirm a real persistence need. Decide whether the design needs multiple persistence strategies or a meaningful domain-to-infrastructure boundary rather than protection against a hypothetical migration.
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