I am not an great at linq by any means but I usually have no issues with a problem of this sort. I want to convert this foreach statement to a LINQ statement:
var existingKeys = new List<int>();
foreach (var taskKey in request.Keys)
{
existingKeys.AddRange(_context.WebTaskGroups
.Where(x => x.TaskGroupNameKey == key && x.TaskKey == taskKey)
.Select(x => x.TaskGroupNameKey));
}
I thought this would do it:
var existingKeys = request.Keys.ForEach(taskKey => _context.WebTaskGroups
.Where(x => x.TaskGroupNameKey == key && x.TaskKey == taskKey)
.Select(x => x.TaskGroupNameKey));
That apparently returns a void not a list...
This:
var existingKeys = request.Keys.Select(taskKey =>
_context.WebTaskGroups
.Where(x => x.TaskGroupNameKey == key && x.TaskKey == taskKey)
.Select(keys => keys.TaskGroupNameKey));
Gives me an "IEnumerable<IQueryable<int>>. So what is the secret sauce that I am missing here?
You shouldn't be performing N database queries in the first place. Using LINQ to perform those N queries instead of a foreach loop doesn't fix that core problem.
You need to re-conceptualize your query so that you have just one query that gets all of the data that you need. In this case that means getting all of the items that match your collection of keys rather than trying to match a single key and then performing N of those queries.
var requestedKeys = request.Keys;
var existingKeys = _context.WebTaskGroups
.Where(x => x.TaskGroupNameKey == key &&
requestedKeys.Contains(x.TaskKey))
.Select(x => x.TaskGroupNameKey))
.ToList();
var existingKeys = request
.SelectMany(r => r.Keys)
.SelectMany(tk =>
_context.WebTaskGroups
.Where(x.TaskGroupNameKey == key && x.TaskKey == tk)
.Select(x => x.TaskGroupNameKey))
.ToList();
var existingKeys = _context.WebTaskGroups
.Where(x => x.TaskGroupNameKey == key && request.Keys.Contains(x.TaskKey))
.Select(x => x.TaskGroupNameKey)
.ToList();
ForEach return a void: http://msdn.microsoft.com/en-us/library/bwabdf9z(v=vs.110).aspx
ForEch: Performs the specified action on each element of the List.
So what to do, is for each item in the list of request.Keys to perform the action to add to the list of existingKeys.
For example:
request.Keys.ForEach(taskKey =>
existingKeys.AddRange(_context.WebTaskGroups
.Where(x => x.TaskGroupNameKey == key && x.TaskKey == taskKey)
.Select(x => x.TaskGroupNameKey));
Related
I have the following Entity Framework 2.0 query:
var user = context.Users.AsNoTracking()
.Include(x => x.UserSkills).ThenInclude(x => x.Skill)
.Include(x => x.UserSkills).ThenInclude(x => x.SkillLevel)
.FirstOrDefault(x => x.Id == userId);
var userSkills = user.UserSkills.Select(z => new {
SkillId = z.SkillId,
SkillLevelId = z.SkillLevelId
}).ToList()
Then I tried the following query:
var lessons = _context.Lessons.AsNoTracking()
.Where(x => x.LessonSkills.All(y =>
userSkills.Any(z => y.SkillId == z.SkillId && y.SkillLevelId <= z.SkillLevelId)))
.ToList();
This query evaluates locally and I get the message:
The LINQ expression 'where (([y].SkillId == [z].SkillId) AndAlso ([y].SkillLevelId <= [z].SkillLevelId))' could not be translated and will be evaluated locally.'.
I tried to solve it using userSkills instead of user.UserSkills but no luck.
Is there a way to run this query on the server?
You should try limiting the usage of in-memory collections inside LINQ to Entities queries to basically Contains on primitive value collection, which currently is the only server translatable construct.
Since Contains is not applicable here, you should not use the memory collection, but the corresponding server side subquery:
var userSkills = context.UserSkills
.Where(x => x.UserId == userId);
var lessons = context.Lessons.AsNoTracking()
.Where(x => x.LessonSkills.All(y =>
userSkills.Any(z => y.SkillId == z.SkillId && y.SkillLevelId <= z.SkillLevelId)))
.ToList();
or even embed the first subquery into the main query:
var lessons = context.Lessons.AsNoTracking()
.Where(x => x.LessonSkills.All(y =>
context.UserSkills.Any(z => z.UserId == userId && y.SkillId == z.SkillId && y.SkillLevelId <= z.SkillLevelId)))
.ToList();
Use Contains on the server then filter further on the client:
var userSkillIds = userSkills.Select(s => s.SkillId).ToList();
var lessons = _context.Lessons.AsNoTracking()
.Where(lsn => lsn.LessonSkills.All(lsnskill => userSkillIds.Contains(lsnskill.SkillId)))
.AsEnumerable() // depending on EF Core translation, may not be needed
.Where(lsn => lsn.LessonSkills.All(lsnskill => userSkills.Any(uskill => uskill.SkillId == lsnskill.SkillId && lsnskill.SkillLevelId <= uskill.SkillLevelId)))
.ToList();
var listOfIds = new List<string>();
var allItems = IEnumerable<Info>();
foreach (var id in collectionIds)
{
listOfIds.AddRange(allItems
.Where(p => p.Data.FirstOrDefault(m => m.Key == "myId").Value == id)
.Select(x => x.Id));
}
I would like to avoid using AddRange but use only Add in this case and maybe use only FirstOrDefault in the place of where to avoid the last Select case.
Is this possible and if yes how?
Assuming your original code is giving you the correct data, specifically you are OK with:
Only concerned that the first item in p.Data contains a matching value and;
p.Data will always contains at least a single element.
Then this code will give you the same output:
var listOfIds = allItems
.Where(p => collectionIds.Contains(p.Data.First(m => m.Key == "myId").Value))
.ToList();
However, if you really do care that any value in p.Data matches, then this would be more appropriate:
var listOfIds = allItems
.Where(p => p.Data.Any(m => m.Key == "myId" &&
collectionIds.Contains(m.Value)))
.ToList();
How about this approach:
var listOfIds = new List<string>();
var allItems = IEnumerable<Info>();
var groupedAllItems = allItems.GroupBy(x => x.Data.FirstOrDefault(m => m.Key == "myId")?.Value ?? "MyIdNotFound");
//collectionIds should be of type HashSet<string> for the contains to be fast
listOfIds.AddRange(groupedAllItems.Where(x => collectionIds.Contains(x.Key)).SelectMany(x => x));
I am trying to remove an item from a list. It finds the item with the above query, but it doesn't remove it from the list. I don't know why is it so?
var qry = db.AssemblyListItems
.AsNoTracking()
.Where(x => x.ProductionPlanID == (long)_currentPlan.ProductionPlan)
.ToList();
var hasbeenAssembled = db.Assembleds
.AsNoTracking()
.Where(x => x.ProductionPlanId == (long)_currentPlan.ProductionPlan)
.ToList();
foreach (var item in hasbeenAssembled)
{
qry = qry.RemoveAll(X => X.DocumentNo == item.DocumentId &&
X.ItemCode == item.KitHeaderId &&
X.ProductionPlanID == item.ProductionPlanId );
}
olvData.SetObjects(qry);
Above is a listView where i want the items to appear. The main query "qry" is on the top.
You can handle this all in one query by excluding the assembled items from the list in a subquery:
var productionPlan = (long)_currentPlan.ProductionPlan;
var qry = db.AssemblyListItems
.AsNoTracking()
.Where(item => item.ProductionPlanID == productionPlan
&& !db.Assembleds
.Any(x => x.ProductionPlanId == item.ProductionPlanID
&& x.DocumentNo == item.DocumentId
&& x.ItemCode == item.KitHeaderId))
The advantage is (as also said by others) that you don't pull AssemblyListItems into memory that you're going to discard again later. Entity Framework will be able to translate this into one SQL statement, so everything is handled efficiently by he database.
Don't include the unwanted items in the results of the query. Don't prematurely bring over query results from the database when it might be able to process the query for you.
var hasBeenAssembled = db.Assembleds
.AsNoTracking()
.Where(x => x.ProductionPlanId == (long)_currentPlan.ProductionPlan);
var qry = db.AssemblyListItems
.AsNoTracking()
.Where(x => x.ProductionPlanID == (long)_currentPlan.ProductionPlan)
.Where(ali => !hasBeenAssembled.Any(hba => hba.DocumentId == ali.DocumentNo && hba.KitHeaderId == ali.ItemCode && hba.ProductionPlanId == ali.ProductionPlanID))
.ToList();
olvData.SetObjects(qry);
Easier way to do this. Items in the first list does not exist in the second list.
from item in hasbeenAssembled
where !(qry.Any(X => X.DocumentNo == item.DocumentId &&
X.ItemCode == item.KitHeaderId &&
X.ProductionPlanID == item.ProductionPlanId))
select item;
I am trying to find the indexes as follows.
But the following LINQ says there is no extension of FindIndex.
foreach (var distinctClassId in distinctClassIds)
{
var indexes = classComponents.Where(x=> x.ClassId.Equals(distinctClassId)).
FindIndex(x => x.Id == Constants.Classes.ClassID.ToString() ||
x.Id == Constants.Courses.CoursesID.ToString());
}
FindIndex() is an instance method of List<T>. But Where() returns an IEnumerable<T> (or maybe an IQueryable<T> depending on what classComponents is in your code).
So you need to convert that Where result to list before you can call FindIndex():
foreach (var distinctClassId in distinctClassIds)
{
var indexes = classComponents.Where(x=> x.ClassId.Equals(distinctClassId)).ToList(). // here -> ToList()
FindIndex(x => x.Id == Constants.Classes.ClassID.ToString() ||
x.Id == Constants.Courses.CoursesID.ToString());
}
But FindIndex() only gives you the index of the first matching item. Your variable is called indexes, so you might want to find the indices of multiple matching items. This can be done by using the linq overloads that give you the index, too:
foreach (var distinctClassId in distinctClassIds)
{
var filtered = classComponents.Where(x=> x.ClassId.Equals(distinctClassId)).ToList();
var indexes = filtered.Select((item, index) => new {item, index})
.Where(x => x.item.Id == Constants.Classes.ClassID.ToString() ||
x.item.Id == Constants.Courses.CoursesID.ToString())
.Select(x => x.index);
}
This creates objects of anonymous type containing the item and its index, then checking which items match and finally returning their indices.
Note: if you actually wanted the indices in the source list (classComponents), you should combine the Where statements like that:
foreach (var distinctClassId in distinctClassIds)
{
var indexes = classComponents.Select((item, index) => new {item, index})
.Where(x => x.item.ClassId.Equals(distinctClassId) &&
(x.item.Id == Constants.Classes.ClassID.ToString() ||
x.item.Id == Constants.Courses.CoursesID.ToString()))
.Select(x => x.index);
}
What I'm doing now is getting my SQL database table: IsAcross varchar(45) into my if/else statement. My IsAcross table only consist of YES and NO.
So now I want to take out only select YES statement from SQL Server, so therefore I have put the thingy in the whole list first. Then I use if/else statement to extract out the YES but how am I supposed to do that?
Example: I have a total of 7 items in a list, 4 yes 3 no. I want to take out the all the 4 yes only. Something like that:
ViewModels.WordSearchVM wsvm = new ViewModels.WordSearchVM();
wsvm.ActivityID = id;
var results = db.CrossPuzzles.Where(m => m.ActivityID == id)
.Select(m => m.IsAcross)
.AsEnumerable()
.ToList();
if (results = "yes")
{
else
}
As far as I understand your problem, you can forget your if statement and simply extend the .Where part:
.Where(m => m.ActivityID == id && m.results=="yes")
var results = db.CrossPuzzles.Where(m => m.ActivityID == id)
.Where(m => m.IsAcross)
.AsEnumerable()
.ToList();
//OR
var results = db.CrossPuzzles.Where(m => m.ActivityID == id)
.Where(m => m.IsAcross == "YES")
.AsEnumerable()
.ToList();
var results = db.CrossPuzzles
.Where(m => m.ActivityID == id)
.Select(m => m.IsAcross)
.Where(x => x == "YES") // filter to "YES"
.ToList();
if (results.Count > 0)
// YES
else
// NO
This what you're looking for?