Linq to Entities Search Algorithm
I'm implementing a search that will take six possible (but not required) user inputs and then try to match them to some entities.
I think the issue I have come up against is that EF and SQL Server think of nulls as two very different things.
Idea: select an entity where columnA = (if columnA is null then columnA (or null) else searchTerm). The search terms are a mix of ints and strings.
Some code:
entities= (from c in context.Entities
where c.ColumnA == (searchTermA ?? v.ColumnA)
where c.ColumnB == (开发者_开发技巧searchTermB ?? v.ColumnB)
select new
{
v.Property,
}).ToList();
If all columns do not contain nulls, entities are returned. However, I do not get expected results if the column has nulls.
How can I work around this?
Richard
This is what i used to handle null values. It was the only way i could get the right results.
((searchTermA.HasValue) ? (c.ColumnA == searchTermA) : true)
Have the function accept a Predicate<T>
and do the construction of the filter on the UI side.
See: http://msdn.microsoft.com/en-us/library/bfcke1bz.aspx
The easy way is this one:
var query = from c in context.Entities;
if (searchTermA != null) {
query = query.Where(c => c.ColumnA == searchTermA);
}
// Rest of your conditions defined in the same way.
var entities = query.Select(c => new { c.Property }).ToList();
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