Entity Framework Core Extensions: Getting Primary Keys and Dirty Properties

Friday, November 10, 2017

Two simple hacks: finding the primary key values:

public static IDictionary<string, object> GetKeys(this DbContext ctx, object entity)
{
    if (ctx == null)
    {
        throw new ArgumentNullException(nameof(ctx));
    }

    if (entity == null)
    {
        throw new ArgumentNullException(nameof(entity));
    }
    
    var entry = ctx.Entry(entity);
    var primaryKey = entry.Metadata.FindPrimaryKey();
    var keys = primaryKey.Properties.ToDictionary(x => x.Name, x => x.PropertyInfo.GetValue(entity));

    return keys;
}

This returns a dictionary because some entities may have composite primary keys.

As for getting the dirty (modified) properties’ names for an entity:

public static IEnumerable<string> GetDirtyProperties(this DbContext ctx, object entity)
{
    if (ctx == null)
    {
        throw new ArgumentNullException(nameof(ctx));
    }

    if (entity == null)
    {
        throw new ArgumentNullException(nameof(entity));
    }

    var entry = ctx.Entry(entity);
    var originalValues = entry.OriginalValues;
    var currentValues = entry.CurrentValues;

    foreach (var prop in originalValues.Properties)
    {
        if (object.Equals(originalValues[prop.Name], currentValues[prop.Name]) == false)
        {
            yield return prop.Name;
        }
    }
}

Picking on the last one, if we wish to reset an entity to it’s original values:

public static void Reset(this DbContext ctx, object entity)
{
    if (ctx == null)
    {
        throw new ArgumentNullException(nameof(ctx));
    }

    if (entity == null)
    {
        throw new ArgumentNullException(nameof(entity));
    }

    var entry = ctx.Entry(entity);
    var originalValues = entry.OriginalValues;
    var currentValues = entry.CurrentValues;

    foreach (var prop in originalValues.Properties)
    {
        currentValues[prop.Name] = originalValues[prop.Name];
    }

    entry.State = EntityState.Unchanged;
}