CODEWITHSUNDEEP
c#.netlinqentity-frameworkdynamic
Tom
Tom

Reputation: 1763

Dynamic conditions in Linq-to-Entities query

I'm trying to convert some old code that directly builds SQL queries to Entity Framework, and came across a problem that many seem to have (judging from the large number of questions surround that topic): how to express dynamic where conditions in linq.

How could I express the following code with a linq query:

    switch (status) {
        case "0":
            sqlwhere = " WHERE status < 0 ";
            break;
        case "-1":
            sqlwhere = " WHERE status = -1 ";
            break;
        case "-100":
            sqlwhere = " WHERE status = -100 ";
            break;
        case "1":
        default:
            sqlwhere = " WHERE status >= 0 ";
            break;
    }

    if (strsearch != "")
        sqlwhere += " AND desc LIKE '%" + strsearch + "%' ";

    string sqlc = "SELECT top 10 * FROM c " + sqlwhere + " order by date desc";

I've read about PredicateBuilder and the dynamic Linq extensions in other posts, but I think that a simple case like could be solvable without external libraries.

Using .net 4.5, EF 5.0, C#, can this be done in a "dynamic" way without building the complete linq statement for each single case?

Upvotes: 4

Views: 5596

Answers (3)

Khalil10
Khalil10

Reputation: 69

you can use LinkExtension with LinqKit 

  using (var context = new workEntities() )
{

    Dictionary<string, List<string>> dictionary = new Dictionary<string, List<string>>();
    dictionary["Title"] = new List<string> {  
                    "Network Engineer", 
                    "Security Specialist", 
                    "=Web Developer"
                };
    dictionary["Salary"] = new List<string> { ">=2000" };
    dictionary["VacationHours"] = new List<string> { ">21" };
    dictionary["SickLeaveHours"] = new List<string> { "<5" };                
    dictionary["HireDate"] = new List<string> { 
                    ">=01/01/2000",
                    "28/02/2014" 
                };
    dictionary["ModifiedDate"] = new List<string> { DateTime.Now.ToString() };

    var data = context.Employee.CollectionToQuery(dictionary).ToList();
}

Upvotes: 0

Sergey Berezovskiy
Sergey Berezovskiy

Reputation: 236208

If you don't want to use something external, then simply use fluent API:

var query = db.YourTableName
              .Where(x => x.desc.Contains(strsearch));

switch (status) {
   case "0":
        query = query.Where(x => x.status < 0);
        break;
   case "-1":
        query = query.Where(x => x.status == -1);
        break;
   case "-100":
        query = query.Where(x => x.status == -100);
        break;
   case "1":
   default:
        query = query.Where(x => x.status >= 0);
        break;
}

var result = query.OrderByDescending(x => x.date)
                  .Take(10);

BTW You can create extension method for filtering by status. And your query will look like:

var query = db.YourTableName
              .FilterByStatus(status)
              .Where(x => x.desc.Contains(strsearch))
              .OrderByDescending(x => x.date)
              .Take(10);

Extension method:

public static IQueryable<YourType> FilterByStatus(this IQueryable<YourType> query, 
                                                  string status)
{

    switch (status) {
       case "0":
            return query.Where(x => x.status < 0);            
       case "-1":
            return query.Where(x => x.status == -1);
       case "-100":
            return query.Where(x => x.status == -100);
       case "1":
       default:
            return query.Where(x => x.status >= 0);
    }
}

Upvotes: 2

Pranay Rana
Pranay Rana

Reputation: 176896

In your case make use of PredicateBuilder like as below

Also check my blog post : Dynamic query with Linq

var outer = PredicateBuilder.True<Entity>();

switch (status) {
        case "0":
            outer = outer.And (p => p.status<0);
            break;
        case "-1":
            outer = outer.And (p => p.status==-1);
            break;
        case "-100":
            outer = outer.And (p => p.status==-100);
            break;
        case "1":
        default:
            outer = outer.And (p => p.status>=0); 
            break;
    }

if (strsearch != "")
        outer = outer.And (p => p.desc.Contains(strsearch ));

dataContext.Entity.Where (outer );

Upvotes: 2

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