A custom CQRS library for .NET can be worthwhile when a codebase has recurring needs that a small, consistent abstraction can solve. It is not automatically better than using an existing mediator or framework—and the available facts do not establish the author’s library, implementation, or personal reason for creating it. What they do establish is the architectural choice at the heart of CQRS: separate command and query responsibilities without assuming separate databases, event sourcing, or a large framework.
What is CQRS in .NET?
CQRS stands for Command Query Responsibility Segregation. It separates operations that change state (commands) from operations that return information (queries). In a .NET application, that can mean different request handlers, models, and code paths for writes and reads. It does not, by itself, prescribe a particular library or deployment architecture.
As an Amazon Associate I earn from qualifying purchases.
Microsoft’s simplified CQRS example in eShopOnContainers separates queries and client-facing ViewModels from commands, the domain model, and transactions, while using one database. The split is logical: each side can be designed for its responsibility without requiring physically distinct systems. Microsoft Learn’s simplified CQRS and DDD guidance presents this as a practical arrangement, not a mandate for every application.
Free tools Windows power users keep installed
One-click scans. No signup required.
Do I need separate databases for CQRS?
No. A single database can support distinct command and query models. Separate read and write stores are an optional, more elaborate topology, not a prerequisite for CQRS. Splitting storage adds coordination and consistency concerns; it should answer a concrete need rather than serve as a definition of the pattern. Event sourcing is also optional.
#1 Best Overall
Microsoft’s simplified example uses one database with two logical models. A query path may read across tables or aggregates and shape the response for a particular client, while the transactional write path preserves the domain’s rules. Microsoft describes read-side options including Dapper, another micro-ORM, EF Core, or plain ADO.NET. The query mechanism can therefore differ from the write-side persistence approach without requiring another database. The Microsoft Learn guide describes these implementation choices.
What should a CQRS library make explicit?
A library is useful only insofar as its abstractions make the application clearer or easier to maintain. Before building one, identify the repeated decisions it will standardize. The architectural choices below are not universal rules; they are places where a library can either provide a helpful convention or conceal a meaningful tradeoff.
Query results: dynamic shapes or explicit DTOs
Dynamic query results can make early iteration quicker because a developer need not update a ViewModel class whenever the SQL result changes. The tradeoff is less clarity for developers and consumers, weaker client compatibility, and less descriptive Swagger documentation. Explicit DTOs give the API a visible contract and support richer documentation, but changes to the response require corresponding maintenance.
Microsoft’s reference application began with dynamic ViewModels and later moved to explicit DTOs as its API stabilized. That is a useful lifecycle option: optimize for iteration while a response is unsettled, then make the contract explicit when consumers depend on it. Microsoft’s CQRS guide explains this tradeoff.
Rank #3
Side effects: domain events or integration events
A domain event records something that happened within the domain and can make resulting side effects explicit. Domain events are commonly handled in-process and can be synchronous or asynchronous. Microsoft’s reference application uses MediatR to propagate synchronous domain events within a single transaction.
An integration event communicates a committed change across bounded contexts or system boundaries and is asynchronous. That can reduce the impact of database locks and support scalability, but it means consumers may observe changes later. The design must account for eventual consistency and what happens when a workflow fails, including whether compensating actions are needed. These event types solve different problems; a library should not blur the boundary between an in-process domain action and cross-service communication. Microsoft Learn’s domain events guidance covers the distinction.
Persistence: repositories or direct access
Repositories around aggregate roots are one option for transactional updates, while CQRS can use separate query paths. But repository abstractions are a design choice, not a consensus requirement. Microsoft’s persistence guidance discusses repositories and also quotes Jimmy Bogard’s preference for MediatR commands and direct use of persistence capabilities, rather than hiding those details behind repositories. The right choice depends on whether the abstraction clarifies the domain and test boundaries or merely obscures the persistence behavior the application needs. Microsoft’s persistence-layer guidance presents both the repository approach and Bogard’s view.
Windows Errors? Fix Them Before They Spread
Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallOutdated Drivers Are Slowing You Down
One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchShould I use MediatR or build my own CQRS library?
That depends on the problem you need to solve. An existing mediator may already cover the dispatch pattern your application needs. A custom library may make sense if several applications or teams repeatedly need the same conventions and you can keep the abstraction focused. Neither option is inherently superior, and CQRS itself does not require a mediator library.
Compare the choices against concrete needs rather than package names: whether handlers and request types are already clear, whether you need a particular convention or integration, and whether the proposed library reduces repetition without making control flow harder to follow. The evidence available here does not identify the author’s library, its API, supported .NET versions, dependencies, tests, limitations, or motivation. Those details—and any comparison with MediatR—cannot be asserted without the project’s documentation or the author’s account.
When is CQRS worth the complexity?
Start with the business and application needs. Microsoft’s DDD guidance says simpler CRUD responsibilities can use simpler approaches; richer domain models and DDD patterns can be useful when a domain is complex and business rules are significant or changing. In that richer design, the application layer coordinates use cases, while domain rules belong in the domain model, which should avoid direct dependencies on infrastructure frameworks. Microsoft Learn’s domain-model guidance describes when that added structure may be appropriate.
- Consider CQRS when reads and writes have meaningfully different responsibilities or need different models.
- Keep a simpler CRUD design when separating those responsibilities would add ceremony without addressing a real problem.
- Do not add separate databases, event sourcing, or cross-service events merely to make an implementation look more like an elaborate CQRS architecture.
- For a custom library, define the repeated problem it solves and check that its abstractions keep request flow, domain behavior, and persistence decisions understandable.
Microsoft’s architecture pages are guidance and examples, not controlled comparisons proving that one design or library performs better. They provide no benchmark basis for claims of speedups or maintenance savings. Any such claim about a particular custom library would need its own reproducible evidence.
The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
