EF Core 8 Primitive collections

What can we do when we want to store a list of primitive types? Before EF Core 8, there were two options:

  • Create a wrapper class and a related table, then add a foreign key linking each value to its owner of the collection.
  • Use value converter to serialize-deserialize as JSON.

The first option covers most scenarios if we need to add some additional properties to this type but let's say we're never gonna need this type additionality.

Which collection types are supported ?

EF Core has the capability to map the IEnumerable<T> public properties that have both a getter and a setter, with the T representing a primitive type

public class PrimitiveCollections
    public IEnumerable<int> Ints { get; set; }
    public ICollection<string> Strings { get; set; }
    public ISet<DateTime> DateTimes { get; set; }
    public IList<DateOnly> Dates { get; set; }
    public uint[] UnsignedInts { get; set; }
    public List<bool> Booleans { get; set; }
    public List<Uri> Urls { get; set; }

Some generic arguments are not considered primitive on the database side, such as uint and Uri. However, these types are also considered as primitive because there are built-in value converters.


In this sample, we have a Car class with a Color enum, and the Car class has a Colors property.

public enum Color

public class Car
    public int Id { get; set; }
    public string Brand { get; set; }
    public string Model { get; set; }
    public ISet<Color> Colors { get; set; } = new HashSet<Color>();

    public Car(string brand, string model)
        Brand = brand;
        Model = model;

When we want to list the cars if they have any of the specific colors.

var colors = new HashSet<Color> { Color.Blue, Color.White };
var cars = await context
    .Where(x=> x.Colors.Intersect(colors).Any())

The SQL result looks like this; as you can see, it sends colors as parameters instead of adding them inline. It also uses the json_each function to deserialize on the database side.

SELECT "c"."Id", "c"."Brand", "c"."Colors", "c"."Model"
      FROM "Cars" AS "c"
          SELECT 1
          FROM (
              SELECT "c0"."value"
              FROM json_each("c"."Colors") AS "c0"
              SELECT "c1"."value"
              FROM json_each(@__colors_0) AS "c1"
          ) AS "t")

When we insert to the car table.

var car = new Car("Maserati", "GranTurismo")
    Colors = new HashSet<Color>()
await context.SaveChangesAsync();

The SQL statement looks like this, and as you can see, it automatically serializes into the Colors parameter as JSON.

 Executed DbCommand (0ms) [Parameters=
 [@p0='Maserati' (Nullable = false) (Size = 8),
  @p1='[0,3]' (Nullable = false) (Size = 5),
  @p2='GranTurismo' (Nullable = false) (Size = 4)
 ], CommandType='Text', CommandTimeout='30']
      INSERT INTO "Cars" ("Brand", "Colors", "Model")
      VALUES (@p0, @p1, @p2)
      RETURNING "Id";


We don't need to do anything if we just use a collection of primitive types. It serializes and deserializes them as JSON automatically. Additionally, it sends the primitive collection as a parameter to cache the query.


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