/// <summary>
/// If the specified property refers to a static LambdaExpression property, this sets result to that expression with the source
/// expression supplied as the lambda parameter.
/// <para/>
/// Example: i.SomeAggregateExpression
/// </summary>
/// <param name="propertyInfo">The property that may or may not contain a LambdaExpression.</param>
/// <param name="source">The expression that will be given to the LambdaExpression as a parameter.</param>
/// <param name="result">If successful, represents the body of a LambdaExpression with the source replacing the original LambdaExpression's parameter.</param>
/// <returns></returns>
private static bool TryGetExpressionProperty(PropertyInfo propertyInfo, Expression source, out Expression result)
{
if (propertyInfo == null)
{
throw new InvalidOperationException($"Property on '{source.Type.FullName}' is not valid");
}
var propertyTypeInfo = propertyInfo.PropertyType;
if (!typeof(Expression).GetTypeInfo().IsAssignableFrom(propertyTypeInfo))
{
result = null;
return(false);
}
if (!typeof(LambdaExpression).GetTypeInfo().IsAssignableFrom(propertyTypeInfo))
{
throw new InvalidOperationException($"Expression properties must return a LambdaExpression. '{propertyInfo.DeclaringType.FullName}.{propertyInfo.Name}'");
}
var property = propertyInfo.GetAccessors().FirstOrDefault();
if (property == null || !property.IsStatic)
{
throw new InvalidOperationException($"Expression properties must be static. '{propertyInfo.DeclaringType.FullName}.{propertyInfo.Name}'");
}
// j => j.SomeAggregateExpression
var lambda = (LambdaExpression)property.Invoke(null, null);
var changer = new ParamChanger(lambda.Parameters[0], source);
// i.SomeAggregateExpression
result = changer.Visit(lambda.Body);
return(true);
}