LINQ to SQL Where Clause Optional Criteria

Solution 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;
}

Solution 2:

Just need to use a conditional checking for the parameter's existence. For instance:

where (string.IsNullOrEmpty(ProductNumber) || ProductNumber == tags.productNumber)

That way if the product number isn't entered that expression will return true in all cases, but if it is entered it will only return true when matching.