Why learning to build your own ORM is worth it (even if you use EF Core or Dapper)

#programming #csharp #sql #orm

Why learning to build your own ORM is worth it (even if you use EF Core or Dapper)

Most developers meet ORMs the same way they meet electricity, you flip a switch and things work. That’s great, until something gets slow, a query behaves oddly, or you hit a transaction or concurrency edge case and you suddenly need to know what’s happening under the hood.

Building a small ORM, even a deliberately limited one, is one of the fastest ways to close the gap between “I can use EF Core or Dapper” and “I understand data access.”

To keep it grounded, I’ll anchor this around my tiny demo ORM (MicroOrm), a .NET 8 sample using SQLite, simple POCOs, a lightweight Include for eager loading, and CancellationToken propagation end to end. (GitHub)

1) You stop treating the database like a black box

When you write mapping yourself, you’re forced to answer questions full ORMs often hide:

What SQL is actually executed?
How are parameters created and bound?
How do nulls map into value types vs nullable types?
What happens when schema changes, column names drift, or types don’t match?
How do you retrieve identities safely after inserts?

This is where “I know EF” turns into “I can debug a data issue under pressure.”

2) Reflection becomes a tool, not a mystery

A tiny ORM almost always starts with reflection.

You inspect a type, find its attributes, discover the key property, build a column list, and map rows back into objects. In MicroOrm’s demo, entities like Blog and Post use familiar attributes like [Table], [Key], [ForeignKey], and [InverseProperty], which is exactly the kind of metadata you typically read via reflection. (GitHub)

The payoff is immediate because you hit two truths fast:

Reflection is powerful, it removes a ton of repetitive glue code.
Reflection is not free, so you learn to cache metadata and keep reflection out of hot paths.

Those instincts carry straight into EF Core too.

3) Generics give you type safety and a clean API surface

Generics are the other superpower of a micro ORM.

They let you write APIs that feel natural in C# and stay strongly typed:

GetById<T>(id) returns a T, not object
GetAll<T>() returns List<T>, not dictionaries
One set of operations can work across your entities without repetition

In practice, building a micro ORM becomes a “generics + reflection” exercise done right, compile-time safety on the outside, runtime discovery on the inside.

4) You finally learn ADO.NET for real (SqlConnection, SqlCommand, and friends)

EF Core and Dapper sit on top of ADO.NET. When you build your own ORM, you stop skipping the fundamentals:

Connections (SqlConnection, SqliteConnection, or DbConnection)
You learn what “open late, close early” actually looks like, why using or await using matters, and how connection pooling changes the way you should think about lifetime.
Commands (SqlCommand, DbCommand)
You get comfortable with parameterized queries (and why they’re non negotiable), command timeouts, and how provider differences show up.
Readers (DbDataReader)
You learn what streaming results means, how mapping happens row by row, and where conversions and null handling can bite you.
Transactions (DbTransaction)
You start treating transaction boundaries as a deliberate design choice, not an incidental side effect of the ORM.

MicroOrm’s demo explicitly highlights cancellation support across opening connections and executing commands, which is exactly the sort of detail you only appreciate once you’re directly using these classes. (GitHub)

5) You learn the real price of convenience (and why loading strategy matters)

MicroOrm’s Include supports both references and collections, implemented as extra queries per entity. It’s intentionally simple, and extremely educational because you can feel the tradeoff immediately: clearer code and predictable behavior, plus a very real risk of N+1 query explosions if you’re not careful. (GitHub)

After you build even a basic Include, you start spotting inefficient loading patterns everywhere, including in mature ORMs.

6) You learn portability the honest way

“Database agnostic” always has seams.

The sample calls it out plainly: switching from SQLite to SQL Server means swapping the provider and adjusting identity retrieval in SqlBuilder.Insert to use SELECT SCOPE_IDENTITY();. That single detail teaches a big lesson, database behavior differences are real and they show up fast. (GitHub)

The takeaway

Writing a tiny ORM is not about shipping a competitor to EF Core.

It’s about gaining X-ray vision for what’s underneath, reflection, generics, ADO.NET primitives like SqlConnection and SqlCommand, query cost, round trips, and transactions. Then, when you choose EF Core or Dapper, you’re not just using them, you’re using them with intent.