How to build up conditional queries with a mix of OR and AND clauses?

Hi, I'm trying to implement a search feature where the user can specify one or more search criteria in a form, and then perform conditional AND and OR logic to build the correct search query to load an Entity.

What is the best way to do this? I've read through the User Guide but it's not obvious to me how to combine a bunch of WHERE clauses where some use AND and some use OR, within the same query.

For example, the user can enter a "keyword" and also an optional "category". The "keyword" should match on ("Title" OR "Description") AND (CategoryId).

You should be able to achieve this fairly easily by building up the QueryExpression as required, e.g. assume you have a Dictionary of key value pairs for field names and user supplied values to search on you can do something like this in code:

var query = new Query(typeof(MyEntity));

foreach (var kvp in dictionary)
{
  query.QueryExpression = query.QueryExpression && Entity.Attribute(kvp.Key) == kvp.Value;
}

You can adjust the operator use etc accordingly.

In terms of specifying the query you mentioned above, you can specify this as:

query.QueryExpression =  ((Entity.Attribute("Title") == keyword || Entity.Attribute("Description") == keyword) && Entity.Attribute("CategoryId") == categoryId);

So when specifying your query expression you can use brackets to maintain the structure of the expression you desire.

Jeremy