select from a list with field name and field value with linq (similar to select command)

Question

I want to select from a dynamic list where the list field name is for example 'SecName'and the SecName value is equal to for example 'xxx', I know how to create it in sql, but I want to create and use it with entity framework. Like Executing String in sql. How can I make it in entity framework and linq. It should be something like this

var lst=_efmodel.Tables.where(x=>x.fieldname=="SecName" && x.value=="xxx").tolist();

I'm looking for syntax to filter my list by passing two string, 1st string should be property Name and the Other should be that property value.

That is not trivial, not maintainable and generally a bad idea. Consider remodelling your database or restructuring your code so you don't need it. It would help if you could show an example of _why_ you need this. Anyway see [How to create an expression at runtime](http://stackoverflow.com/questions/19164308/how-to-create-an-expression-at-runtime-for-use-in-groupby-with-entity-framewor), [Building dynamic where clauses in LINQ to EF queries](http://stackoverflow.com/questions/14901430/), and so on. — CodeCaster, Oct 18 '15 at 09:47

score 2 · Answer 1 · answered Oct 18 '15 at 13:43

After searching I found the Answer ,Answer is:

     public class SearchField
    {
        public string Name { get; set; }
        public string @Value { get; set; }
        //public string Operator { get; set; }

        public SearchField(string Name, string @Value)
        {
            this.Name = Name;
            this.@Value = @Value;
            //Operator = "=";
        }
    }
    public class FilterLinq<T>
    {
        public static Expression<Func<T, Boolean>> GetWherePredicate(params SearchField[] SearchFieldList)
        {

            //the 'IN' parameter for expression ie T=> condition
            ParameterExpression pe = Expression.Parameter(typeof(T), typeof(T).Name);

            //combine them with and 1=1 Like no expression
            Expression combined = null;

            if (SearchFieldList != null)
            {
                foreach (var fieldItem in SearchFieldList)
                {
                    //Expression for accessing Fields name property
                    Expression columnNameProperty = Expression.Property(pe, fieldItem.Name);


                    //the name constant to match 
                    Expression columnValue = Expression.Constant(fieldItem.Value);

                    //the first expression: PatientantLastName = ?
                    Expression e1 = Expression.Equal(columnNameProperty, columnValue);

                    if (combined == null)
                    {
                        combined = e1;
                    }
                    else
                    {
                        combined = Expression.And(combined, e1);
                    }
                }
            }

            //create and return the predicate
            if (combined != null) return Expression.Lambda<Func<T, Boolean>>(combined, pe);
            return null;
        }

    }

and use it like this :

var lst = _efmodel.Count(2015).AsQueryable()
                                    .Where(
          FilterLinq<PazTedad_Result>.GetWherePredicate(
          new SearchField("FieldName", "FieldValue"))).ToList();

Mykola · Answer 2 · 2015-10-18T13:16:19.383

0

Code must be something like this?

var lst=_efmodel.Table.Where(x => x.fieldname == <SomeValue>).ToList();

edited Oct 18 '15 at 13:16

answered Oct 18 '15 at 09:51

Mykola

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Its general template of calling linq. I do not know exact name of fields wich you have used. I am gust making suggestions with code from your post. – Mykola Oct 18 '15 at 13:08
I'm Not sure that my code is correct or not, I gust maybe it's should be look like this,I'm looking for the Correct syntax , I want a syntax to filter my list by two string,First is column Name and the second is that column value. – Hootan.Ghiasi Oct 18 '15 at 13:13
If you think in that way it, changes everything – Mykola Oct 18 '15 at 13:15
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/92646/discussion-between-hootan-ghiasi-and-mykola). – Hootan.Ghiasi Oct 18 '15 at 13:19

select from a list with field name and field value with linq (similar to select command)

2 Answers2