If statements within a Linq where clause - linq

Question

Struggling a bit today.
I have the following method that returns a list of products..lovely.
public static List<tblWeight> GetProductInfo(string memberid, string locationid, string basematerial, string source)
{
MyEntities getproductinfo = new MyEntities ();
return (from p in getproductinfo .tblWeights
where p.MemberId == memberid &&
p.LocationId == locationid &&
p.BaseMaterialName == basematerial &&
p.WeightStatus == source
select p)
.ToList();
Where basematerial & source are drop down lists.
How do I go about incorporating a few IF statements into the where clause?
For example, if the basematerial ddl is not touched but an item in the source ddl is selected, the result would return everything associated with basematerial but filtered by the selected source.
Does that even make sense?!
I'm not even sure I am taking the correct approach - please forgive my ignorance.

Answer 1

you can add them to your query on need:
var r = (from p in getproductinfo .tblWeights
where p.MemberId == memberid &&
p.LocationId == locationid &&
p.WeightStatus == source
select p)
if (!String.IsNullOrEmpty(basematrial))
r = r.Where(p => p.BaseMaterialName == basematerial);
return r.ToList();

Answer 2

Consider implementing these extension methods named WhereIf.
You pass it two parameters: a statement evaluated to a boolean, and a lambda function. If the bool statement evaluates to true, the lambda is added.
WhereIf on ExtensionMethod.net
Your query could look like:
return getproductinfo.tblWeights
.Where(w=> w.MemberId == memberid &&
w.LocationId == locationid)
.WhereIf(!string.IsNullOrEmpty(basematerial), w=>w.BaseMaterialName == basematerial)
.WhereIf(!string.IsNullOrEmpty(source), w=>w.WeightStatus == source)
.ToList();
Here they are, for both IEnumerable and IQueryable. This allows you to use .WhereIf() in LINQ To SQL, Entity Framework, Lists, Arrays, and anything else that implements those 2 interfaces.
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;
}
public static IEnumerable<TSource> WhereIf<TSource>(this IEnumerable<TSource> source, bool condition, Func<TSource, int, bool> predicate)
{
if (condition)
return source.Where(predicate);
else
return source;
}
public static IQueryable<TSource> WhereIf<TSource>(this IQueryable<TSource> source, bool condition, Func<TSource, bool> predicate)
{
if (condition)
return source.Where(predicate);
else
return source;
}
public static IQueryable<TSource> WhereIf<TSource>(this IQueryable<TSource> source, bool condition, Func<TSource, int, bool> predicate)
{
if (condition)
return source.Where(predicate);
else
return source;
}