Question
I'm using the Dynamic Linq Library in my .NET MVC application to query a SQL Server database. It's all working fine so far.
I need to make a dynamic select but always return Expression of type 'T' expected:
public static IQueryable<T> SelectByFields<T>(this IQueryable<T> q, string expression, params object[] values) // IEnumerable<string> fieldNames)
{
try
{
var param = Expression.Parameter(typeof(T), "p");
var lambda = System.Linq.Dynamic.DynamicExpression.ParseLambda(new ParameterExpression[] { param }, typeof(T), expression, values);
Type[] types = new Type[] { q.ElementType, lambda.Body.Type };
return q.Provider.CreateQuery<T>(Expression.Call(typeof(Queryable), "Select", types, q.Expression, Expression.Quote(lambda)));
}
catch
{
return q;
}
Accepted Answer
Finally I solve the problem
public static IQueryable SelectByFields(this IQueryable q, string expression, params object[] values) // IEnumerable<string> fieldNames)
{
try
{
if (q == null)
throw new ArgumentNullException("source");
if (expression == null)
throw new ArgumentNullException("selector");
LambdaExpression lambda = System.Linq.Dynamic.DynamicExpression.ParseLambda(q.ElementType, null, expression, values);
Type[] types = new Type[] { q.ElementType, lambda.Body.Type };
return q.Provider.CreateQuery(Expression.Call(typeof(Queryable), "Select", types, q.Expression, Expression.Quote(lambda)));
}
catch
{
return q;
}
}
And call to method
var aux = context.CLIENTES.SelectByFields("new (ID)") as IQueryable<Object>;
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