linq2db.EntityFrameworkCore

linq2db.EntityFrameworkCore is an integration of LINQ To DB with existing EntityFrameworkCore projects. It was inspired by this issue in EF.Core repository.

Build status

Feeds

NuGet
Azure Artifacts (feed)

Unique features

Fast Eager Loading (incomparable faster on massive Include query)
Global Query Filters optimization
Better SQL optimization
Use CTE in LINQ queries
MERGE statement support
Table hints
Full Window functions support
Fast BulkCopy of millions records
Native SQL operations for updating, deleting, inserting records via LINQ query
Temporary Tables support
Cross Database/Linked Server queries.
Full Text Search extensions
A lot of extensions to cover ANSI SQL

How to use

In your code you need to initialize integration using following call:

LinqToDBForEFTools.Initialize();

After that you can just call DbContext and IQueryable extension methods, provided by LINQ To DB.

You can also register additional options (like interceptors) for LinqToDB during EF context registration, here is an example:

var optionsBuilder = new DbContextOptionsBuilder<MyDbContext>();
optionsBuilder.UseSqlite();
optionsBuilder.UseLinqToDB(builder =>
{
    // add custom command interceptor
    builder.AddInterceptor(new MyCommandInterceptor());
    // add additional mappings
    builder.AddMappingSchema(myCustomMappings);
    // configure SQL Server dialect explicitly
    //builder.AddCustomOptions(o => o.UseSqlServer(SqlServerVersion.v2022));
    // due to bug in linq2db 5.0.0, use overload with connection string
    // will be fixed in next linq2db release
    builder.AddCustomOptions(o => o.UseSqlServer("unused", SqlServerVersion.v2022));
});

There are many extensions for CRUD Operations missing in vanilla EF (watch our video):

// fast insert big recordsets
ctx.BulkCopy(new BulkCopyOptions {...}, items);

// query for retrieving products that do not have duplicates by Name
var query =
    from p in ctx.Products
    from op in ctx.Products.LeftJoin(op => op.ProductID != p.ProductID && op.Name == p.Name)
    where Sql.ToNullable(op.ProductID) == null
    select p;

// insert these records into the same or another table
query.Insert(ctx.Products.ToLinqToDBTable(), s => new Product { Name = s.Name ... });

// update these records by changing name based on previous value
query.Update(prev => new Product { Name = "U_" + prev.Name ... });

// delete records that matched by query
query.Delete();

Some extensions require LINQ To DB ITable<T> interface, which could be acquired from DbSet<T> using ToLinqToDBTable() extension method.

For ITable<T> interface LINQ To DB provides several extensions that may be useful for complex databases and custom queries:

table = table.TableName("NewTableName");     // change table name in query
table = table.DatabaseName("OtherDatabase"); // change database name, useful for cross database queries.
table = table.OwnerName("OtherOwner");       // change owner.

// inserting into other existing table Products2
query.Insert(ctx.Products.ToLinqToDBTable().TableName("Products2"), s => new Product { Name = s.Name ... });

It is not required to work directly with LINQ To DB DataConnection class but there are several ways to do that. LINQ To DB will try to reuse your configuration and select appropriate data provider:

// uing DbContext
using (var dc = ctx.CreateLinqToDBConnection())
{
   // linq queries using linq2db extensions
}

// using DbContextOptions
using (var dc = options.CreateLinqToDBConnection())
{
   // linq queries using linq2db extensions
}

You can use all LINQ To DB extension functions in your EF linq queries. Just ensure you have called ToLinqToDB() function before materializing objects for synchronous methods.

Since EF Core have defined it's own asynchronous methods, we have to duplicate them to resolve naming collisions. Async methods have the same name but with LinqToDB suffix. E.g. ToListAsyncLinqToDB(), SumAsyncLinqToDB(), ect. The same methods are added whe you need EF Core query processing but there is collision with LINQ To DB and they have extensions with EF suffix - ToListAsyncEF(), SumAsyncEF(), ect.

using (var ctx = CreateAdventureWorksContext())
{
    var productsWithModelCount =
        from p in ctx.Products
        select new
        {
            // Window Function
            Count = Sql.Ext.Count().Over().PartitionBy(p.ProductModelID).ToValue(),
            Product = p
        };

    var neededRecords =
        from p in productsWithModelCount
        where p.Count.Between(2, 4) // LINQ To DB extension
        select new
        {
            p.Product.Name,
            p.Product.Color,
            p.Product.Size,
            // retrieving value from column dynamically
            PhotoFileName = Sql.Property<string>(p.Product, "ThumbnailPhotoFileName")
        };

    // ensure we have replaced EF context
    var items1 = neededRecords.ToLinqToDB().ToArray();       
    
    // async version
    var items2 = await neededRecords.ToLinqToDB().ToArrayAsync(); 
    
    // and simple bonus - how to generate SQL
    var sql = neededRecords.ToLinqToDB().ToString();
}

Also check existing tests in test project for some examples.

Why should I want to use it?

There are many reasons. Some of them:

you want to use advanced SQL functionality, not supported or poorly supported by EntityFrameworkCore like BulkCopy support, SQL MERGE operations, convinient DML (Insert/Delete/Update) operations and many-many-many other features LINQ To DB provides, but you need change tracking functionality that EntityFramework provides.
you want to migrate to LINQ To DB, but need to do it step-by-step.
just because LINQ To DB is cool.

Current status

Below is a list of providers, that should work right now:

SQL Server
MySQL (including Devart and Pomelo providers)
PostgreSQL (Both npgsql and Devart providers)
SQLite (including Devart provider)
Firebird
DB2 LUW
Oracle
SQL Server CE

Known limitations

No Lazy loading
No way to work with in-memory database
No TPT (table per type) support
No many-to-many support

Help! It doesn't work!

If you encounter any issue with this library, first check issues to see if it was already reported and if not, feel free to report new issue.

code-sujan/linq2db.EntityFrameworkCore