LINQ to SQL Where Clause Optional Criteria

Question

I am working with a LINQ to SQL query and have run into an issue where I have 4 optional fields to filter the data result on. By optional, I mean has the choice to enter a value or not. Specifically, a few text boxes that could have a value or have an empty string and a few drop down lists that could have had a value selected or maybe not...

For example:

    using (TagsModelDataContext db = new TagsModelDataContext())      {         var query = from tags in db.TagsHeaders                     where tags.CST.Equals(this.SelectedCust.CustCode.ToUpper())                      && Utility.GetDate(DateTime.Parse(this.txtOrderDateFrom.Text)) <= tags.ORDDTE                     && Utility.GetDate(DateTime.Parse(this.txtOrderDateTo.Text)) >= tags.ORDDTE                     select tags;         this.Results = query.ToADOTable(rec => new object[] { query });     } 

Now I need to add the following fields/filters, but only if they are supplied by the user.

1. Product Number - Comes from another table that can be joined to TagsHeaders.
2. PO Number - a field within the TagsHeaders table.
3. Order Number - Similar to PO #, just different column.
4. Product Status - If the user selected this from a drop down, need to apply selected value here.

The query I already have is working great, but to complete the function, need to be able to add these 4 other items in the where clause, just don't know how!

Answer 1

You can code your original query:

var query = from tags in db.TagsHeaders                 where tags.CST.Equals(this.SelectedCust.CustCode.ToUpper())                  && Utility.GetDate(DateTime.Parse(this.txtOrderDateFrom.Text)) <= tags.ORDDTE                 && Utility.GetDate(DateTime.Parse(this.txtOrderDateTo.Text)) >= tags.ORDDTE                 select tags; 

And then based on a condition, add additional where constraints.

if(condition)     query = query.Where(i => i.PONumber == "ABC");  

I am not sure how to code this with the query syntax but id does work with a lambda. Also works with query syntax for the initial query and a lambda for the secondary filter.

You can also include an extension method (below) that I coded up a while back to include conditional where statements. (Doesn't work well with the query syntax):

        var query = db.TagsHeaders             .Where(tags => tags.CST.Equals(this.SelectedCust.CustCode.ToUpper()))             .Where(tags => Utility.GetDate(DateTime.Parse(this.txtOrderDateFrom.Text)) <= tags.ORDDTE)             .Where(tags => Utility.GetDate(DateTime.Parse(this.txtOrderDateTo.Text)) >= tags.ORDDTE)             .WhereIf(condition1, tags => tags.PONumber == "ABC")             .WhereIf(condition2, tags => tags.XYZ > 123); 

The extension method:

public static IQueryable<TSource> WhereIf<TSource>(     this IQueryable<TSource> source, bool condition,     Expression<Func<TSource, bool>> predicate) {     if (condition)         return source.Where(predicate);     else         return source; } 

Here is the same extension method for IEnumerables:

public static IEnumerable<TSource> WhereIf<TSource>(     this IEnumerable<TSource> source, bool condition,     Func<TSource, bool> predicate) {     if (condition)         return source.Where(predicate);     else         return source; }