Entity Framework Core tries to reinsert navigation property on save after AddRange

Question

I have the following model:

[Table("Facts")]
public partial class Facts
{
  [Key]
  public Guid ID { get; set; }
  public Guid UserID { get; set; }
  [ForeignKey(nameof(UserID))]
  public Users Users { get; set; }
  //other properties are ommitted
}

Its migration code:

migrationBuilder.CreateTable(
            name: "Facts",
            columns: table => new
            {
                ID = table.Column<Guid>(nullable: false),
                UserID = table.Column<Guid>(nullable: false),
            //other properties are ommitted
            },
            constraints: table =>
            {
                table.PrimaryKey("PK_Facts", x => x.ID);
                table.ForeignKey(
                    name: "FK_Facts_Users_UserID",
                    column: x => x.UserID,
                    principalTable: "Users",
                    principalColumn: "ID",
                    onDelete: ReferentialAction.Cascade);
            });

As it has a navigation property, I set it to an existing ID (it is required).

This is the saving method:

 public async Task SaveData<T>(List<T> data, bool isNew) where T : class
 {
   if (data == null)
      throw new ArgumentNullException(nameof(data));
   try
   {
     if (isNew)
       context.Set<T>().AddRange(data);
     else
     {
       context.Set<T>().AttachRange(data);
       data.ForEach(d => (context as DbContext).Entry(d).State = EntityState.Modified);
     }
     await context.SaveChangesAsync();
   }
   catch (Exception ex)
   {       
     throw;
   }
 }

When I enter the save method, I have the following state (the ID is set, the navigation property object is null):

After AddRange , I have the following state (the ID is set, the navigation property object is not null ):

Inside the catch, I get the following exception:

Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for details. ---> Microsoft.Data.Sqlite.SqliteException: SQLite Error 19: 'FOREIGN KEY constraint failed'

It looks like it tries to add the navigation property object as a new item to the database.

How can I prevent the reinsert of the already existing navigation property?

UPDATE

After enabling the SQL logging, I get the following information (@p0 is the PK, @p18 is the FK):

Failed executing DbCommand (105ms) [Parameters=[@p0='84ddca86-3f8a-41f1-aaed-2c65bd1cb384' (DbType = String),...@p18='e33f7939-bc35-4d82-b68b-e1cc0cf32ff1' (DbType = String)...]
INSERT INTO "Facts" ("ID", ... "UserID",...)
      VALUES (@p0, @p1, @p2, @p3, @p4, @p5, @p6, @p7, @p8, @p9, @p10, @p11, @p12, @p13, @p14, @p15, @p16, @p17, @p18, @p19, @p20, @p21, @p22, @p23, @p24, @p25, @p26, @p27, @p28, @p29);
Microsoft.Data.Sqlite.SqliteException (0x80004005): SQLite Error 19: 'FOREIGN KEY constraint failed'.

UPDATE2

I made some emulator testing and I found out the following.

The data of Users table is inserted initially via a SQL script, with the following code:

public async virtual Task ExecuteCommandAsync(string sqlCommand)
{
  await context.Database.ExecuteSqlCommandAsync(new RawSqlString(sqlCommand));
}

As you can see, the record exists:

When I save an unrelated data with SaveData , its ID is stored as binary data :

So maybe Entity Framework Core is somehow confused when trying to convert binary data to text? Still don't know why retrieve works normally then.

Answer 1

It is a problem with ef core when using it in a non awaited asyncron task or in other concurrent scenarios. Try awaiting save changes.

EDIT: It does have another case when is behaving like this, the case when you are using data from 2 different dbContext instances.