LINQ实体框架动态查询

Question

I have two Guid collections:

List<Guid> statuses;
List<Guid> priorities;

How to make the following query:

var result = context.Activity.Where(a => 
    (a.StatusID == statuses[0] || a.StatusID == statuses[1] || ... || a.StatusID == statuses[n]) &&
    (a.PriorityID == priorities[0] || a.PriorityID == priorities[1] || ... || a.PriorityID  == priorities[m]))

Collections could be empty and in this case we shouldn't add an appropriate 'AND' condition. How to do such dynamic query?

UPDATE

Hmm, imagine I need something like this:

List<Func<Activity, bool>> conds = new List<Func<Activity, bool>>();

var result = context.Activity.Where(conds[0] || (conds[1] && conds[2]))

How to do that?

Answer 1

First answer based on question
Selects only those Activity objects of which the StatusID is in statusses and the PriorityID is in priorities . Obviously if the collections are empty none of the Activity objects will match the condition.

var result = context.Activity.Where(a => 
    statuses.Contains(a.StatusID) && priorities.Contains(a.PriorityID));

Alternative answer based on @Don Tomato's comment
There must have been a misunderstanding based on the way you formulated the question. However, I think what you want is to add conditions to an IQueryable as required.

List<Func<Activity, bool>> conditions = new List<Func<Activity, bool>>();
// add conditions to the list
// for eaxmple:
// conditions.add(a => statuses.Contains(a.StatusID));
// or 
// conditions.add(a => a.Name == "Don Tomato");

IQueryable query = context.Activity.AsQueryable();
foreach (Func<Activity, bool> condition in conditions)
   query = query.Where(condition);

List<Activity> result = query.ToList();

Answer 2

You can chain where clauses together like this and the end result is that they will be anded together:

var query = context.Activity.Where(o => <condition1>);

if (2ndconditionrequired)
{
    query = query.where(o => <condition2>);
}

query.ToList();

Answer 3

You could also do it like this:

var result = context.Activity;

if (statuses != null && statuses.Count > 0)
{
    result = results.Where(a => 
        a.StatusID == statuses[0] || a.StatusID == statuses[1] || ... || a.StatusID == statuses[n];
}

if (priorities != null && priorities.Count > 0)
{
    result = results.Where(a => 
        a.PriorityID == priorities[0] || a.PriorityID == priorities[1] || ... || a.PriorityID  == priorities[m]);
}

result.ToList(); // The query won't be executed until here.

But I guess what you really want to do is as @Bazzz answered.