Dynamic WHERE clause in LINQ

Question

What is the best way to assemble a dynamic WHERE clause to a LINQ statement?

I have several dozen checkboxes on a form and am passing them back as: Dictionary<string, List<string>> (Dictionary<fieldName,List<values>>) to my LINQ query.

public IOrderedQueryable<ProductDetail> GetProductList(string productGroupName, string productTypeName, Dictionary<string,List<string>> filterDictionary)
{
    var q = from c in db.ProductDetail
            where c.ProductGroupName == productGroupName && c.ProductTypeName == productTypeName
            // insert dynamic filter here
            orderby c.ProductTypeName
            select c;
    return q;
}

Solution 1

_{(source: scottgu.com)}

You need something like this? Use the Linq Dynamic Query Library (download includes examples).

Check out ScottGu's blog for more examples.

Solution 2

I have similar scenario where I need to add filters based on the user input and I chain the where clause.

Here is the sample code.

var votes = db.Votes.Where(r => r.SurveyID == surveyId);
if (fromDate != null)
{
    votes = votes.Where(r => r.VoteDate.Value >= fromDate);
}
if (toDate != null)
{
    votes = votes.Where(r => r.VoteDate.Value <= toDate);
}
votes = votes.Take(LimitRows).OrderByDescending(r => r.VoteDate);

Solution 3

You can also use the PredicateBuilder from LinqKit to chain multiple typesafe lambda expressions using Or or And.

http://www.albahari.com/nutshell/predicatebuilder.aspx

Solution 4

A simple Approach can be if your Columns are of Simple Type like String

public static IEnumerable<MyObject> WhereQuery(IEnumerable<MyObject> source, string columnName, string propertyValue)
{
   return source.Where(m => { return m.GetType().GetProperty(columnName).GetValue(m, null).ToString().StartsWith(propertyValue); });
}

Solution 5

It seems much simpler and simpler to use the ternary operator to decide dynamically if a condition is included

List productList = new List();

        productList =
                db.ProductDetail.Where(p => p.ProductDetailID > 0 //Example prop
                && (String.IsNullOrEmpty(iproductGroupName) ? (true):(p.iproductGroupName.Equals(iproductGroupName)) ) //use ternary operator to make the condition dynamic
                && (ID == 0 ? (true) : (p.ID == IDParam))
                ).ToList();

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Comments

[Ryan Gates]

There is a ported version on github (github.com/kahanu/System.Linq.Dynamic), which I contribute to and help manage.

[user6121177]

Best suited for my need and easy to use. Thank you.

[FelixSFD]

A link to a solution is welcome, but please ensure your answer is useful without it: add context around the link so your fellow users will have some idea what it is and why it’s there, then quote the most relevant part of the page you're linking to in case the target page is unavailable. Answers that are little more than a link may be deleted.

[KJM]

I do apologize. I am new here.

[khalil]

possible to do other than string ?

[Sushant Yelpale]

brilliant Answer !!

[harvzor]

My application is complaining that this can't be translated to SQL (I'm using Postgres provider). Perhaps your code is running in memory rather than on the db? This would lead to bad performance on large datasets.

[MtnManChris]

Both links are not completely valid. Scott Guthrie's Blog is missing the code and the System.Linq.Dyanmic is a 404