How to create a Linq expression tree that compares with a shared object?

Question

I have an IQueryable and an object of type T.

I want to do IQueryable (). Where (o => o.GetProperty (fieldName) == objectOfTypeT.GetProperty (fieldName))

So...

public IQueryable<T> DoWork<T>(string fieldName)
        where T : EntityObject
{
   ...
   T objectOfTypeT = ...;
   ....
   return SomeIQueryable<T>().Where(o => o.GetProperty(fieldName) == objectOfTypeT.GetProperty(fieldName));
}

Fyi, GetProperty is not a valid function. I need something that performs this function.

Do I have a Friday brain on Friday, or is it a tricky thing?

---

objectOfTypeT I can do the following ...

var matchToValue = Expression.Lambda(ParameterExpression
.Property(ParameterExpression.Constant(item), "CustomerKey"))
.Compile().DynamicInvoke();

Which works fine, now I just need the second part:

return SomeIQueryable (). Where (o => o.GetProperty (fieldName) == matchValue);

Answer 1

Same:

    var param = Expression.Parameter(typeof(T), "o");
    var fixedItem = Expression.Constant(objectOfTypeT, typeof(T));
    var body = Expression.Equal(
        Expression.PropertyOrField(param, fieldName),
        Expression.PropertyOrField(fixedItem, fieldName));
    var lambda = Expression.Lambda<Func<T,bool>>(body,param);
    return source.Where(lambda);

, , .

- , , objectOfTypeT ( ), Expression.Constant, , " ".

Answer 2

, , - ...

IQueryable<T>().Where(t => 
MemberExpression.Property(MemberExpression.Constant(t), fieldName) == 
ParameterExpression.Property(ParameterExpression.Constant(item), fieldName));

, , .

Answer 3

What about:

    public class Person
    {
        public string Name { get; set; }
        public int Age { get; set; }

    }

    public Func<T, TRes> GetPropertyFunc<T, TRes>(string propertyName)
    {
        // get the propertyinfo of that property.
        PropertyInfo propInfo = typeof(T).GetProperty(propertyName);

        // reference the propertyinfo to get the value directly.
        return (obj) => { return (TRes)propInfo.GetValue(obj, null); };
    }

    public void Run()
    {
        List<Person> personList = new List<Person>();

        // fill with some data
        personList.Add(new Person { Name = "John", Age = 45 });
        personList.Add(new Person { Name = "Michael", Age = 31 });
        personList.Add(new Person { Name = "Rose", Age = 63 });

        // create a lookup functions  (should be executed ones)
        Func<Person, string> GetNameValue = GetPropertyFunc<Person, string>("Name");
        Func<Person, int> GetAgeValue = GetPropertyFunc<Person, int>("Age");


        // filter the list on name
        IEnumerable<Person> filteredOnName = personList.Where(item => GetNameValue(item) == "Michael");
        // filter the list on age > 35
        IEnumerable<Person> filteredOnAge = personList.Where(item => GetAgeValue(item) > 35);
    }

This is a way to get property values ​​row by row without using dynamic queries. The disadvantage is that all values ​​will be in the box / unpacked.