EF Core Query Discover the Basics about Querying a Database in LINQ

Entity Framework Core uses Language Integrate Query (LINQ) to query data from the database.

• LINQ allows you to use C# (or your .NET language of choice) to write strongly typed queries based on your derived context and entity classes.
• Querying in Entity Framework Core remains the same as in EF 6 to load entities from the database.
• It provides more optimized SQL queries and the ability to include C#/VB.NET functions into LINQ-to-Entities queries.

Let's say we have a simple model which contains three entities.

public class Customer
{
    public int CustomerId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Address { get; set; }
    public virtual List<Invoice> Invoices { get; set; }
}

Load All data

The following example load all the data from Customers table.

using (var context = new MyContext())
{
    var customers = context.Customers.ToList();
}

Load a Single Entity

The following example load a single record from Customers table based on CustomerId.

using (var context = new MyContext())
{
    var customers = context.Customers
        .Single(c => c.CustomerId == 1);
}

Filter Data

The following example loads all customers with FirstName Mark.

using (var context = new MyContext())
{
    var customers = context.Customers
        .Where(c => c.FirstName == "Mark")
        .ToList();
}