Open source object-relational mapping framework for ADO.NET.
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Pro Migrations API
List all versions of a schema, apply one or go back to a previous version.
Pro Database support
Supports most popular databases.
Better than the chaotic and confusing NHibernate documentation.
Pro Typesafe queries
Linq2Sql allows writing queries using the actual ORM types. This prevents issues when modifying the schema/entities.
Pro Avoids creation of inline SQL queries
No longer do you have to create/close SQL connections every time you want to interact with the database. You also don't have to maintain a database reader to handle the results retrieved from the database; all of this functionality is easily handled through LINQ queries and Entity Framework.
Pro Database agnostic
You can quite easily migrate from using one DB technology to another.
Pro Non intrusive object model
Object model is non-intrusive and consistent.
For simple data storage scenarios, EF may be unnecessarily complicated to learn.
Micro-ORMs have better performance.