Linq Expression Tree String Comparison

Question

I am trying to build an expression tree to work with a string array. I need to figure out how to use the Equal method.

Can someone give me an example 1) using the Expression.Equal (or .Equals) method to compare a string with a constant and
2) using an expression of any type to use the string.Contains () method for filtering purposes.

I am trying to learn the mechanics of Expression Tree, but have not yet found a good tutorial. I really appreciate your help.

string[] arr = {"s1","s2","s3"};
IQueryable<String> queryableData = arr.AsQueryable<string>();

// what should go below here?
ParameterExpression p1 = Expression.Parameter(typeof(string), "c");
Expression left = Expression.Constant("s2");
Expression e1 = Expression.Equal(left, p1);

IQueryable<string> res = queryableData.Provider.CreateQuery<string>(e2);

Answer 1

, , ... , , .NET . Queryable.Where() queryableData ... , .NET , - :

MethodCallExpression call = Expression.Call(
    null, // Calling Queryable.Where(), extension method, not instance method
    getGenericMethod<string>(typeof(Queryable), "Where", typeof(IQueryable<string>), typeof(Expression<Func<string,bool>>)),
    Expression.Constant(queryableData),
    Expression.Lamda(
       e1,
       p1)
);
IQueryable<string> res = queryableData.Provider.CreateQuery<string>(call);

getGenericMethod ( , ):

private static MethodInfo getGenericMethod<T>(Type type, string name, params Type[] paramTypes)
{
    MethodInfo[] methods = type.GetMethods(name);
    foreach(MethodInfo mi in methods)
    {
        if(!mi.IsGenericMethodDefinition) // or some similar property
            continue;
        if(mi.GetGenericArguments().Length != 1)
            continue;
        if(mi.GetParameters().Length != paramTypes.Length)
            continue;


        MethodInfo genMethod = mi.MakeGenericMethod(new Type[]{typeof(T)});
        var ps = genMethod.GetParameters();
        bool isGood = true;
        for(int i = 0; i < ps.Length; i++)
        {
            if(ps[i].ParameterType != paramTypes[i])
            {
               isGood = false;
               break;
            }
        }

        if(isGood)
            return genMethod;

    }

    return null;
}

, , , ...

Answer 2

, :

string[] arr = {"s1","s2","s3"};
IQueryable<String> queryableData = arr.AsQueryable<string>();
ParameterExpression pe = Expression.Parameter(typeof(string), "company");
Expression right = Expression.Constant("on");
Expression left = Expression.Call(pe, typeof(string).GetMethod("Contains"), right);
MethodCallExpression e2 = Expression.Call(
            typeof(Queryable),
            "Where",
            new Type[] { queryableData.ElementType },
            queryableData.Expression,
            Expression.Lambda<Func<string, bool>>(left, new ParameterExpression[] { pe }));

IQueryable<string> res = queryableData.Provider.CreateQuery<string>(e2);