LINQ is it possible to add where clauses dynamically

Question

I want to search my db with different keys. According to the input, there may be 1 key to 10 keys. Is there a way to add OR/AND clauses to my Linq query dynamically?

 keys[k] // I have my keys in this array 
 var feedList = (from feed in ctx.Feed
                 where feed.content.contains(keys[0]) 
                       && feed.content.contains(keys[1])
                       && ... // continues with the keys.length
                 select new {
                    FeedId = feed.DuyuruId,
                    FeedTitle = feed.FeedTitle,
                    FeedContent = feed.FeedContents,
                    FeedAuthor = user.UserName + " " +User.UserSurname
 }

Solution 1

You could try an .All clause to check all the keys:

where keys.All(key => feed.content.contains(key))

Solution 2

For AND clauses it is simple:

var feedList = from feed in ctx.Feed;
foreach(var key in keys){
    feedList = feedList.Where(x=> content.contains(key));
}
var resultQuery = feedList.Select(x=> new {....});

For OR you will need to use Expressions or try LinqKit and its predicates :

var predicate = PredicateBuilder.False<TypeOfYourEntity>();
foreach(var key in keys){
    predicate = predicate.Or(x=> content.contains(key));
}
var resultQuery = ctx.Feed.Where(predicate).Select(x=> new {....});

Solution 3

You can use the extension methods of LINQ

ctx.Feed.Where(f => {  
//Your logic here
if(something != null){
      return f.Property == something
  } 
}).Select( new { FeedId = feed.DuyuruId,
                    FeedTitle = feed.FeedTitle,
                    FeedContent = feed.FeedContents,
                    FeedAuthor = user.UserName + " " +User.UserSurname })

Solution 4

You can do something like this. Remember it may casue some overhead

 var students = ctx.Students;

 if (!String.IsNullOrWhiteSpace(SearchParams.Name))
      students = from s in students where s.Name.StartsWith(SearchParams.Name)

 if (!String.IsNullOrWhiteSpace(SearchParams.Surname))
      students = from s in students where s.Surname.StartsWith(SearchParams.Surname)

Solution 5

I wanted to provide an example of how @mellamokb's answer worked for my scenario to possibly help out anyone needing a fairly dynamic linq query.

In my example I have simply made an extension of the datatable class so I can check if a row of data exists as it stands in the database so no SQL primary key exceptions are thrown.

/// <summary>
/// 
/// </summary>
/// <param name="DT"></param>
/// <param name="ColumnNames">Columns to check in affected table.</param>
/// <param name="ItemtoChecks">Values to check in affected column.</param>
/// <returns></returns>
public static bool TableContains(this DataTable DT, string[] ColumnNames, object[] ItemtoChecks)
{
  var result = from row in DT.AsEnumerable()
               where ColumnNames.All(
               r => row.Field<object>(r).ToString() == Convert.ToString(
                 ItemtoChecks[ColumnNames.ToList()
                 .FindIndex(p => p.Equals(r, StringComparison.OrdinalIgnoreCase))]))
               select row;                   
  return (result.Count() > 0);
}

This method allows you to add as many column names as you require to a string[] along with the corresponding values to check in a separate object[]. The query checks against the datatable and if it finds a match the method returns true and if not it returns false.

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