Basic Querying

Entity Framework Core uses Language-Integrated Query (LINQ) to query data from the database. EF Core passes a representation of the LINQ query to the database provider. Database providers in turn translate it to database-specific query language (for example, SQL for a relational database). Queries are always executed against the database even if the entities returned in the result already exist in the context.

The following snippets show a few examples of how to achieve common tasks with Entity Framework Core.

Loading all data

using (var context = new BloggingContext())
{
    var blogs = context.Blogs.ToList();
}

Loading a single entity

using (var context = new BloggingContext())
{
    var blog = context.Blogs
        .Single(b => b.BlogId == 1);
}

Find()

The Find method on DbSet uses the primary key value to attempt to find an entity tracked by the context. If the entity is not found in the context then a query will be sent to the database to find the entity there. Null is returned if the entity is not found in the context or in the database.

Filtering

using (var context = new BloggingContext())
{
    var blogs = context.Blogs
        .Where(b => b.Url.Contains("dotnet"))
        .ToList();
}

Ordering

Ordering can be done via the OrderBy method. To for instance order a set of authors by last name and then first name we can do the following:

var authorsByLastName = _context.Author
    .OrderBy(a => a.LastName)
    .ThenBy(a => a.FirstName)
    .ToList();