Entity Code First String FK values Uppercase or Lowercase - ef-code-first

Question

FK is linked to tbWarehouseUser 1 recording.
There are both lowercase and uppercase values in the tbWarehouseUser table.
How can I solve this problem ?
The classes are as follows;
private void Form1_Load(object sender, EventArgs e)
{
var model = new Model1();
var tbWarehouse = model.tbWarehouse.Where(c=> c.sWarehouse == "A1").FirstOrDefault();
var tbWarehouseUserList = tbWarehouse.tbWarehouseUser.ToList();
}
tbWarehouseUserList.Count record count 1.
1 record is coming. This problem causes sourced?
Recording picture
public partial class tbWarehouse
{
tbWarehouse()
{
tbWarehouseUser = new HashSet<tbWarehouseUser>();
}
[Key]
[StringLength(4)]
public string sWarehouse { get; set; }
public string WarehouseDescription { get; set; }
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
public virtual ICollection<tbWarehouseUser> tbWarehouseUser { get; set; }
}
public partial class tbWarehouseUser
{
[Key]
[Column(Order = 0)]
[StringLength(4)]
public string sUserName { get; set; }
[Key]
[Column(Order = 1)]
[StringLength(4)]
public string sWarehouseName { get; set; }
public string sUserPass { get; set; }
public virtual tbWarehouse tbWarehouse { get; set; }
}
public partial class Model1 : DbContext
{
public Model1()
: base("name=Model1")
{
}
protected void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<tbWarehouse>()
.Property(e => e.sWarehouse)
.IsFixedLength()
.IsUnicode(false);
modelBuilder.Entity<tbWarehouse>()
.Property(e => e.WarehouseDescription)
.IsUnicode(false);
modelBuilder.Entity<tbWarehouse>()
.HasMany(e => e.tbWarehouseUser)
.WithRequired(e => e.tbWarehouse)
.HasForeignKey(e => e.sWarehouseName)
.WillCascadeOnDelete(false);
modelBuilder.Entity<tbWarehouseUser>()
.Property(e => e.sUserName)
.IsFixedLength()
.IsUnicode(false);
modelBuilder.Entity<tbWarehouseUser>()
.Property(e => e.sWarehouseName)
.IsFixedLength()
.IsUnicode(false);
modelBuilder.Entity<tbWarehouseUser>()
.Property(e => e.sUserPass)
.IsFixedLength()
.IsUnicode(false);
}
}