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# Sunday, November 30, 2014

Farewell Entity Framework and hello Dapper!

For many years we were using Entity Framework. It's still very popular and Microsoft's primary Object-Relational Mapper library.

Clearly, the decision is subjective but here are our arguments.

We know and love SQL, and think that in its domain it occupies strong positions. What SQL leaves out of scope is a bridge between itself and other languages. That's where ORM should help.

We strongly beleive that no ORM library should try to hide SQL behind the Object's language itself. We beleive in a separation of roles in development. Database design and Data Access Layer should be separated from client's logic. Thus, we strive, if possible, to encapulate data access through SQL functions and stored procedures.

Entity Framework, in contrast, tries to factor out SQL, giving a perspective of object graph to a client. Initially, it looks promising but at the end a developer should remember that any object query is mapped back to SQL. Without keeping this in mind either query won't compile, or performance will be poor.

E.g. This query will probably fail to build SQL, as no Regex can be mapped to SQL:

var result = context.Content.
  Where(data => Regex.IsMatch(data.Content, pattern)).
  ToArray();

This query might be slow, if no suitble SQL index is defined:

var result = context.Content.
  Where(data => data.Field == value).
  ToArray();

Thus no EF's goal is achieved completely, SQL power is limitted, and Data Access Layer is often fused into other client's logic.

We think that Entity Framework is over-engineered library, which tries to be more than ORM. Its generality often bumps into limits of SQL support in EF: SQL dialects, types, operators, functions, and so on. One can observe that people for years appeal to introduce support of xml, hierarchyid, geometry/geography types, full text search, and so on. This state cannot be different, as EF will never be able and does not aim to support all SQL features.

EF has both design-time and runtime. Each database vendor should implement their EF adapter for EF to play well with that database. This cooperation is not always smooth. E.g see Database first create entity framework 6.1.1 model using system.data.sqlite 1.0.93.

At some point the cost of dealing with EF has became too high for us, so we started to look into an alternatives: from plain ADO.NET to lighter ORM library.

To our delight we have immediately found: Dapper - a simple object mapper for .NET. It provides a simple extensions to IDBConnection interface to deal with mapping of query parameters to object properties, and of query results to plain types. Here are some examples:

// Get Customer
var customer = connection.
  Query<Customer>("select * from Customers where CustomerId = @id", new { id = customerID }).
  ToSingle();

// Insert a value
connection.Execute("insert into MyTable(A, B) values(@a, @b)", new { a = 2, b = 3 });

So, Dapper leaves you with plain SQL, which we consider as advantage.

Except beeing minimalistic compared to EF, Dapper claims performance close to pure hand written ADO.NET. Indeed, they build dynamic methods to populate parameters and to create rows instances, so reflection is used during warm up period only.

Sunday, November 30, 2014 12:47:46 PM UTC  #    Comments [0] -
.NET | Thinking aloud
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