Expression API to build linq query

[dbjoe]

Hello,

I'm looking for some help with this problem that I am having. I am trying to build a dynamic where clause for Entity Framework using the Expression API. I have a dictionary that contains the following as an example:

myDictionary.Add("ColumnName1", "Column1Value")
myDictionary.Add("ColumnName2", "Column2Value")

I would like the output of the expression to be like this: "x.ColumnName1 == Column1Value AND x.ColumnName2 == Column2Value "

In my code I have tried to keep it simple and use Lists<string>, But ideally I would like to use my dictionary as shown in the above example

    var xParameter = Expression.Parameter(typeof(T), "x"); // x =>
            var keyList = new List<string>();
            var keyValuesList = new List<string>();

            
            foreach(var (Key, value) in keyColumns)
            {
                keyList.Add(Key);
                keyValuesList.Add(value);
            }
                    

                var leftHandSides = keyList.Select(x => Expression.Property(xParameter, x));
                
                var rightHandSide = Expression.Constant(keyValuesList, typeof(List<string>));

            
             var equalityExpressions = leftHandSides.Select(x => Expression.Equal(x, rightHandSide)); //CODE FAILS HERE WITH BINARY ERROR

            var aggregatedExpressions = equalityExpressions.Aggregate((x, y) => Expression.AndAlso(x, y));
        

                return Expression.Lambda<Func<T, bool>>(aggregatedExpressions, xParameter);

I would be grateful for any help on this.

 

[Skydiver]

I doubt that you can do equality checks with lists.

 

[Skydiver]

I know your question was how to build an expression, but out of curiosity: why? It would be infinitely easier to build up a SQL query, and just use raw SQL queries instead.

(You don't know how hard it was for me to write the above to suggest using SQL. I am anti-SQL in an object-oriented world. I believe that if you are using an object-oriented language, you should be playing with objects, and not having to go back to the relational world of SQL or ISAM.)