Improving ObjectQuery.Include – Updated
Having spent some time using the sample from my previous post on ObjectQuery.Include, I’ve encountered a bug! It turns out that the code generates the wrong include string for
context.Customers.Include(c => c.Order.SubInclude(o=>o.OrderDetail))
The fix for this is a small change to the BuildString method to recurse up the MemberExpression if necessary. The updated code is below - usual disclaimers apply!
public static class ObjectQueryExtensions
{
public static ObjectQuery<TSource> Include<TSource, TPropType>(this ObjectQuery<TSource> source, Expression<Func<TSource, TPropType>> propertySelector)
{
string includeString = BuildString(propertySelector);
return source.Include(includeString);
}
private static string BuildString(Expression propertySelector)
{
switch (propertySelector.NodeType)
{
case ExpressionType.Lambda:
LambdaExpression lambdaExpression = (LambdaExpression)propertySelector;
return BuildString(lambdaExpression.Body);
case ExpressionType.Quote:
UnaryExpression unaryExpression = (UnaryExpression)propertySelector;
return BuildString(unaryExpression.Operand);
case ExpressionType.MemberAccess:
MemberExpression memberExpression = (MemberExpression)propertySelector;
MemberInfo propertyInfo = memberExpression.Member;
if (memberExpression.Expression is ParameterExpression)
{
return propertyInfo.Name;
}
else
{
// we've got a nested property (e.g. MyType.SomeProperty.SomeNestedProperty)
return BuildString(memberExpression.Expression) + "." + propertyInfo.Name;
}
case ExpressionType.Call:
MethodCallExpression methodCallExpression = (MethodCallExpression)propertySelector;
if (IsSubInclude(methodCallExpression.Method)) // check that it's a SubInclude call
{
// argument 0 is the expression to which the SubInclude is applied (this could be member access or another SubInclude)
// argument 1 is the expression to apply to get the included property
// Pass both to BuildString to get the full expression
return BuildString(methodCallExpression.Arguments[0]) + "." +
BuildString(methodCallExpression.Arguments[1]);
}
// else drop out and throw
break;
}
throw new InvalidOperationException("Expression must be a member expression or an SubInclude call: " + propertySelector.ToString());
}
private static readonly MethodInfo[] SubIncludeMethods;
static ObjectQueryExtensions()
{
Type type = typeof(ObjectQueryExtensions);
SubIncludeMethods = type.GetMethods().Where(mi => mi.Name == "SubInclude").ToArray();
}
private static bool IsSubInclude(MethodInfo methodInfo)
{
if (methodInfo.IsGenericMethod)
{
if (!methodInfo.IsGenericMethodDefinition)
{
methodInfo = methodInfo.GetGenericMethodDefinition();
}
}
return SubIncludeMethods.Contains(methodInfo);
}
public static TPropType SubInclude<TSource, TPropType>(this EntityCollection<TSource> source, Expression<Func<TSource, TPropType>> propertySelector)
where TSource : class, IEntityWithRelationships
where TPropType : class
{
throw new InvalidOperationException("This method is only intended for use with ObjectQueryExtensions.Include to generate expressions trees"); // no actually using this - just want the expression!
}
public static TPropType SubInclude<TSource, TPropType>(this TSource source, Expression<Func<TSource, TPropType>> propertySelector)
where TSource : class, IEntityWithRelationships
where TPropType : class
{
throw new InvalidOperationException("This method is only intended for use with ObjectQueryExtensions.Include to generate expressions trees"); // no actually using this - just want the expression!
}
}
UPDATE: Alex James has a great post on Eager Loading Strategies that I'd recommend reading.