Best way to check if object exists in Entity Framework?

Question

What is the best way to check if an object exists in the database from a performance point of view? I'm using Entity Framework 1.0 (ASP.NET 3.5 SP1).

Answer 1

If you don't want to execute SQL directly, the best way is to use Any(). This is because Any() will return as soon as it finds a match. Another option is Count(), but this might need to check every row before returning.

Here's an example of how to use it:

if (context.MyEntity.Any(o => o.Id == idToMatch))
{
    // Match!
}

And in vb.net

If context.MyEntity.Any(function(o) o.Id = idToMatch) Then
    ' Match!
End If

Answer 2

From a performance point of view, I guess that a direct SQL query using the EXISTS command would be appropriate. See here for how to execute SQL directly in Entity Framework: http://blogs.microsoft.co.il/blogs/gilf/archive/2009/11/25/execute-t-sql-statements-in-entity-framework-4.aspx

Answer 3

I had to manage a scenario where the percentage of duplicates being provided in the new data records was very high, and so many thousands of database calls were being made to check for duplicates (so the CPU sent a lot of time at 100%). In the end I decided to keep the last 100,000 records cached in memory. This way I could check for duplicates against the cached records which was extremely fast when compared to a LINQ query against the SQL database, and then write any genuinely new records to the database (as well as add them to the data cache, which I also sorted and trimmed to keep its length manageable).

Note that the raw data was a CSV file that contained many individual records that had to be parsed. The records in each consecutive file (which came at a rate of about 1 every 5 minutes) overlapped considerably, hence the high percentage of duplicates.

In short, if you have timestamped raw data coming in, pretty much in order, then using a memory cache might help with the record duplication check.

Answer 4

I know this is a very old thread but just incase someone like myself needs this solution but in VB.NET here's what I used base on the answers above.

Private Function ValidateUniquePayroll(PropertyToCheck As String) As Boolean
    // Return true if Username is Unique
    Dim rtnValue = False
    Dim context = New CPMModel.CPMEntities
    If (context.Employees.Any()) Then ' Check if there are "any" records in the Employee table
        Dim employee = From c In context.Employees Select c.PayrollNumber ' Select just the PayrollNumber column to work with
        For Each item As Object In employee ' Loop through each employee in the Employees entity
            If (item = PropertyToCheck) Then ' Check if PayrollNumber in current row matches PropertyToCheck
                // Found a match, throw exception and return False
                rtnValue = False
                Exit For
            Else
                // No matches, return True (Unique)
                rtnValue = True
            End If
        Next
    Else
        // The is currently no employees in the person entity so return True (Unqiue)
        rtnValue = True
    End If
    Return rtnValue
End Function

Answer 5

I just check if object is null , it works 100% for me

    try
    {
        var ID = Convert.ToInt32(Request.Params["ID"]);
        var Cert = (from cert in db.TblCompCertUploads where cert.CertID == ID select cert).FirstOrDefault();
        if (Cert != null)
        {
            db.TblCompCertUploads.DeleteObject(Cert);
            db.SaveChanges();
            ViewBag.Msg = "Deleted Successfully";
        }
        else
        {
            ViewBag.Msg = "Not Found !!";
        }                           
    }
    catch
    {
        ViewBag.Msg = "Something Went wrong";
    }

Answer 6

I had some trouble with this - my EntityKey consists of three properties (PK with 3 columns) and I didn't want to check each of the columns because that would be ugly. I thought about a solution that works all time with all entities.

Another reason for this is I don't like to catch UpdateExceptions every time.

A little bit of Reflection is needed to get the values of the key properties.

The code is implemented as an extension to simplify the usage as:

context.EntityExists<MyEntityType>(item);

Have a look:

public static bool EntityExists<T>(this ObjectContext context, T entity)
        where T : EntityObject
    {
        object value;
        var entityKeyValues = new List<KeyValuePair<string, object>>();
        var objectSet = context.CreateObjectSet<T>().EntitySet;
        foreach (var member in objectSet.ElementType.KeyMembers)
        {
            var info = entity.GetType().GetProperty(member.Name);
            var tempValue = info.GetValue(entity, null);
            var pair = new KeyValuePair<string, object>(member.Name, tempValue);
            entityKeyValues.Add(pair);
        }
        var key = new EntityKey(objectSet.EntityContainer.Name + "." + objectSet.Name, entityKeyValues);
        if (context.TryGetObjectByKey(key, out value))
        {
            return value != null;
        }
        return false;
    }

Answer 7

Why not do it?

var result= ctx.table.Where(x => x.UserName == "Value").FirstOrDefault();

if(result?.field == value)
{
  // Match!
}

Answer 8

Best way to do it

Regardless of what your object is and for what table in the database the only thing you need to have is the primary key in the object.

C# Code

var dbValue = EntityObject.Entry(obj).GetDatabaseValues();
if (dbValue == null)
{
   Don't exist
}

VB.NET Code

Dim dbValue = EntityObject.Entry(obj).GetDatabaseValues()
If dbValue Is Nothing Then
   Don't exist
End If