SQL Like keyword in Dynamic Linq - dynamic

Question

I want to use SQL's Like keyword in dynamic LINQ.
The query that I want to make is like this
select * from table_a where column_a like '%search%'
Where the column_a can be dynamically changed to other column etc
In this dynamic LINQ
var result = db.table_a.Where( a=> (a.column_a.Contains("search")) );
But the column can't be dynamically changed , only the search key can
How do we create a dynamic LINQ like
var result = db.table_a.Where("column_a == \"search\"");
That we can change the column and the search key dynamically

Answer 1

This should work for you:
.Where("AColumnName.Contains(#0)", "Criteria")

Answer 2

Create an ExtensionMethods class with this function
public static IQueryable<T> Like<T>(this IQueryable<T> source, string propertyName, string keyword)
{
var type = typeof(T);
var property = type.GetProperty(propertyName);
string number = "Int";
if (property.PropertyType.Name.StartsWith(number))
return source;
var parameter = Expression.Parameter(type, "p");
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var constant = Expression.Constant("%" + keyword + "%");
MethodCallExpression methodExp = Expression.Call(null, typeof(SqlMethods).GetMethod("Like", new Type[] { typeof(string), typeof(string) }), propertyAccess, constant);
Expression<Func<T, bool>> lambda = Expression.Lambda<Func<T, bool>>(methodExp, parameter);
return source.Where(lambda);
}
And then call it like this:
var result = db.table_a.Like("column_a", "%search%");

Answer 3

http://weblogs.asp.net/rajbk/archive/2007/09/18/dynamic-string-based-queries-in-linq.aspx
Addition:
Use an expression tree
How do I create an expression tree to represent 'String.Contains("term")' in C#?
That is what the dynamic linq library does internally.

Answer 4

I do not believe there is a direct translation to SQL for the LIKE keyword in LINQ. You could build one if you used expression trees, but I haven't gotten that good yet.
What I do is something like this:
using System.Data.Linq.SqlClient;
if (!string.IsNullOrEmpty(data.MailerName))
search = search.Where(a => SqlMethods.Like(a.Mailer.Name, string.Format("%{0}%", data.MailerName)));
where search is the query I'm building and data is the object containing the properties that hold the search criteria. I build the query dynamically by listing all of the possible search criteria in this way, which adds the appropriate Where methods to search.

Answer 5

Maybe a bit late but Another approach is add Extention method that use Contains to simulate Like keyword as :
public static class DbHelpers
{
public static IQueryable<T> Like<T>(this IQueryable<T> source, string propertyName, string propertyValue)
{
var prop = typeof(T).GetProperty(propertyName);
if (prop == null || prop.PropertyType.Name.StartsWith("Int"))
return source;
ParameterExpression parameter = Expression.Parameter(typeof(T), "row");
Expression property = Expression.Property(parameter, propertyName);
Expression value = Expression.Constant(propertyValue);
var containsmethod = value.Type.GetMethod("Contains", new[] { typeof(string) });
var call = Expression.Call(property, containsmethod, value);
var lambda = Expression.Lambda<Func<T, bool>>(call, parameter);
return source.Where(lambda);
}
}
And use of it:
var foo = entity.AsQueryable().Like("Name", "bla bla");
If send PropertyName with type of int, the method return original entity that you passed before to it.