Dynamic LINQ - Cannot Convert Between GUID and String

Question

I am dynamically creating a LINQ statement. The LINQ statement that I create is used exclusively for the WHERE clause.

string[] values = GetPropertyValues(); 
string propertyName = GetPropertyName();

string clause = string.Empty;
if (values.Length > 0)
  clause = propertyName + "==\"" + values[0] + "\"";

From what I can tell, my LINQ query looks correct. But when it runs, an error message appears:

The operator '==' is not compatible with the operand types 'Guid?' and 'String'

How do I solve this problem?

Thank!

Answer 1

It looks like the property returned by GetPropertyName () is of type Guid (I think from an error), but you are trying to compare it with the contents of the values ​​[0], which you declare as a string.

Dynamic Linq allows you to define parameters in the where clause so you can do

string clause = propertyName + "= @1";
LambdaExpression expr = Dynamic.ParseLambda( typeof(YourType), typeof(bool), clause, values[0]);

YourType - IQueryable. , , IQueyable<Customer>, YourType Customer. , propertyName.

, Dynamic Linq , - YourType propertyName. , , - , .Where().

Answer 2

GUID linq Equals(), .

var items = new[]
            {
                new { Id = Guid.Empty },
                new { Id = Guid.NewGuid() },
                new { Id = Guid.NewGuid() }
            };

var result = items.AsQueryable()
    .Where("Id.Equals(@0)", Guid.Empty)
    .Any();

Answer 3

"Id.Equals(Guid(\"D243372F-7ED0-40E6-B93D-6165F7521C29\"))"

"Value" .

"{ " " " Guid "( 3)}"

Answer 4

- :

clause = "Id.Value.ToString()==\"a\""; /* Id is of type Guid? */

, , .

PredicateBuilder from Albahari may be the best solution overall.

Answer 5

If you don't want to pass guid as a parameter, you can use it to compare strings and pointers:

clause = "Id.Value.Equals(Guid(\"" + values[0] + "\"))";

It works.

... Or this is in your example:

clause = propertyName + ".Value.Equals(\"" + values[0] + "\")";