So I have a Blog object which has a list of tag objects (List<Tag>).
I'm trying to create a method that takes a list of tags and returns a list of blogs that contain all the tags in the passed in list.
I was able to make a method that will return a list of blogs if it matches one tag, but not a list of tags.
to do that I have this
entities.Blogs.Where(b => b.Tags.Any(t => t.Name == tagName))
But I can't figure out how to do something like this
entities.Blogs.Where(b => b.Tags.Any(t => t.Name == tags[0] AND t.Name == tags[1] AND t.Name == tags[2] etc.......))
Is there any way to do this?
Thank you!
I'm using LINQ to Entities
Logically, I think you want something like:
entities.Blogs.Where(b => tags.All(t => b.Tags.Any(bt => bt.Name == t)))
Alternatively:
HashSet<string> tagNames = new HashSet<string>(tags);
return entities.Blogs
.Where(b => tagNames.IsSubsetOf(b.Tags.Select(x => x.Name)));
If this is using LINQ to Entities, I doubt that this will work - but it should work if you're just using LINQ to Objects. Even then, it's not going to be terribly efficient. I suspect there's a more efficient way of doing things, but I can't immediately think of it... it feels like you want a join, but then it gets tricky again.
You can do something like this:
List<Tag> tags = GetTags...;
IQueryable<Blog> blogs = entities.Blogs; // start with all
foreach(var tag in tags){
var thisTag = tag; //this is needed to prevent a bug
blogs = blogs.Where(entry=>entry.Tags.Any(entryTag=>entryTag.TagId==thisTag.TagId));
}
return blogs.OrderBy....;
This will chain together the Where clauses to require that all the Tags be present for a blog entry to be returned.
Related
epublic ActionResult ExistingPolicies()
{
if (Session["UserId"]==null)
{
return RedirectToAction("Login");
}
using(PMSDBContext dbo=new PMSDBContext())
{
List<Policy> viewpolicy = new List<Policy>();
var userid = Session["UserId"];
List<AddPolicy> policy= dbo.AddPolicies.Where(c => c.MobileNumber ==
(string)userid).ToList();
foreach(AddPolicy p in policy)
{
viewpolicy=dbo.Policies.Where(c => c.PolicyId ==p.PolicyId).ToList();
}
Session["Count"] = policy.Count;
return View(viewpolicy);
}
}
Here the policy list clearly has 2 items.But when I iterate through foreach,the viewpolicy list only takes the last item as its value.If break is used,it takes only the first item.How to store both items in viewpolicy list??
Regards
Surya.
You can iterate through policies and add them by one to list with Add, but I would say that often (not always, though) better option would be to just retrieve the whole list from DB in one query. Without knowing your entities you can do at least something like that:
List<AddPolicy> policy = ...
viewpolicy = dbo.Policies
.Where(c => policy.Select(p => p.PolicyId).Contains(c.PolicyId))
.ToList();
But if you have correctly set up entities relations, you should be able to do something like this:
var viewpolicy = dbo.AddPolicies
.Where(c => c.MobileNumber == (string)userid)
.Select(p => p.Policy) //guessing name here, also can be .SelectMany(p => p.Policy)
.ToList();
Of course; instead of adding to the list, you replace it with a whole new one on each pass of the loop:
viewpolicy=dbo.Policies.Where(c => c.PolicyId ==p.PolicyId).ToList()
This code above will search all the policies for the policy with that ID, turn it into a new List and assign to the viewpolicy variable. You never actually add anything to a list with this way, you just make new lists all the time and overwrite the old one with the latest list
Perhaps you need something like this:
viewpolicy.Add(dbo.Policies.Single(c => c.PolicyId ==p.PolicyId));
This has a list, finds one policy by its ID number (for which there should be only one policy, right? It's an ID so I figured it's unique..) and adds it to the list
You could use a Where and skip the loop entirely if you wanted:
viewpolicy=dbo.Policies.Where(c => policy.Any(p => c.PolicyId == p.PolicyId)).ToList();
Do not do this in a loop, it doesn't need it. It works by asking LINQ to do the looping for you. It should be converted to an IN query and run by the DB, so generally more performant than dragging the policies out one by one (via id). If the ORM didn't understand how to make it into SQL you can simplify things for it by extracting the ids to an int collection:
viewpolicy=dbo.Policies.Where(c => policy.Select(p => p.PolicyId).Any(id => c.PolicyId == id)).ToList();
Final point, I recommend you name your "collections of things" with a plural. You have a List<Policy> viewpolicy - this is a list that contains multiple policies so really we should call it viewPolicies. Same for the list of AddPolicy. It makes code read more nicely if things that are collections/lists/arrays are named in the plural
Something like:
viewpolicy.AddRange(dbo.Policies.Where(c => c.PolicyId ==p.PolicyId));
I want to get the company whose employees id card issued with the specific number, sort of finding the exact element inside nested collection.
Using first or default 3 times does not seems to be a correct way.
> var company = cprIdentificationReply.Companies
> .FirstOrDefault(x => (x.Employee
> .FirstOrDefault(y => (y.IDCardIssued
> .FirstOrDefault(z => z.CardNumber
> .Equals(number,StringComparison.InvariantCultureIgnoreCase))) != null)
> != null));
What can be a proper way of achieving the same?
You may want to use the Any extension method:
var companies = cprIdentificationReply.Companies
.Where(x => (x.Employee
.Any(y => (y.IDCardIssued
.Any(z => z.CardNumber
.Equals(number, StringComparison.InvariantCultureIgnoreCase)
)
)
).ToList();
If you want better looking code why don't use LINQ query syntax.
I always find it easier to read LINQ query when looking at someone else's code, especially for complex operations.
Something like this:
var company = (from company in cprIdentificationReply.Companies
from empl in company.Employee
from idCardIss in empl .IDCardIssued
where idCardIss.CardNumber.Equals(number, StringComparison.InvariantCultureIgnoreCase)
select c).FirstOrDefault();
I have a list of Stores (of type ObservableCollection<Store>) and the Store object has a property called Features ( of type List<Feature> ). and the Feature object has a Name property (of type string).
To recap, a list of Stores that has a list of Features
I have a second collection of DesiredFeatures (of type List<string> ).
I need to use LINQ to give me results of only the stores that have all the DesiredFeatures. So far, I've only been able to come up with a query that gives me an OR result instead of AND.
Here's what that looks like:
var q = Stores.Where(s=> s.Features.Any(f=> DesiredFeatures.Contains(f.name)));
I know Intersect can help, and here's how I've used it:
var q = Stores.Where(s => s.Features.Intersect<Feature>(DesiredFeatures));
This is where I'm stuck, Intersect wants a Feature object, what I need to intersect is on the Feature.Name.
The goal is to end up with an ObservableCollection where each Store has all of the DesiredFeatures.
Thank you!
You've almost done what you need. A small refine would be to swap DesiredFeatures and s.Features.
var q = Stores.Where(s => DesiredFeatures.All(df => s.Features.Contains(df)));
It means take only those stores where desired features are all contained in features of the store.
I need to use LINQ to give me results of only the stores that have all the DesiredFeatures.
In other words, each desired feature must have a matching store feature.
I don't see how Intersect can help in this case. The direct translation of the above criteria to LINQ is like this:
var q = Stores.Where(s =>
DesiredFeatures.All(df => s.Features.Any(f => f.Name == df))
);
A more efficient way could be to use a GroupJoin for performing the match:
var q = Stores.Where(s =>
DesiredFeatures.GroupJoin(s.Features,
df => df, sf => sf.Name, (df, sf) => sf.Any()
).All(match => match)
);
or Except to check for unmatched items:
var q = Stores.Where(s =>
!DesiredFeatures.Except(s.Features.Select(sf => sf.Name)).Any()
);
Going on your intersect idea, the only way I thought of making this work was by using Select to get the Store.Features (List<Feature>) as a list of Feature Names (List<string>) and intersect that with DesiredFeatures.
Updated Answer:
var q = Stores.Where(s => s.Features.Select(f => f.Name).Intersect(DesiredFeatures).Any());
or
var q = Stores.Where(s => DesiredFeatures.Intersect(s.Features.Select(f => f.Name)).Any());
Old Answer (if DesiredFeatures is a List<Feature>):
var q = Stores.Where(s => s.Features.Select(f => f.Name).Intersect(DesiredFeatures.Select(df => df.Name)).Any());
Two things you want your code to perform.
var q = Stores.Where(s=> s.Features.All(f=> DesiredFeatures.Contains(f.name)) &&
s.Features.Count() == DesiredFeatures.Count()); // Incude Distinct in the comparison if Features list is not unique
Ensure that every Feature is DesiredFeature
Store contains all Desired features.
Code above assumes uniqueness in Features collection as well as DesiredFeatures, modify code as stated in comment line if this is not right
I need to identify items from one list that are not present in another list. The two lists are of different entities (ToDo and WorkshopItem). I consider a workshop item to be in the todo list if the Name is matched in any of the todo list items.
The following does what I'm after but find it awkward and hard to understand each time I revisit it. I use NHibernate QueryOver syntax to get the two lists and then a LINQ statement to filter down to just the Workshop items that meet the requirement (DateDue is in the next two weeks and the Name is not present in the list of ToDo items.
var allTodos = Session.QueryOver<ToDo>().List();
var twoWeeksTime = DateTime.Now.AddDays(14);
var workshopItemsDueSoon = Session.QueryOver<WorkshopItem>()
.Where(w => w.DateDue <= twoWeeksTime).List();
var matches = from wsi in workshopItemsDueSoon
where !(from todo in allTodos
select todo.TaskName)
.Contains(wsi.Name)
select wsi;
Ideally I'd like to have just one NHibernate query that returns a list of WorkshopItems that match my requirement.
I think I've managed to put together a Linq version of the answer put forward by #CSL and will mark that as the accepted answer as it put me in the direction of the following.
var twoWeeksTime = DateTime.Now.AddDays(14);
var subquery = NHibernate.Criterion.QueryOver.Of<ToDo>().Select(t => t.TaskName);
var matchingItems = Session.QueryOver<WorkshopItem>()
.Where(w => w.DateDue <= twoWeeksTime &&
w.IsWorkshopItemInProgress == true)
.WithSubquery.WhereProperty(x => x.Name).NotIn(subquery)
.Future<WorkshopItem>();
It returns the results I'm expecting and doesn't rely on magic strings. I'm hesitant because I don't fully understand the WithSubquery (and whether inlining it would be a good thing). It seems to equate to
WHERE WorkshopItem.Name IS NOT IN (subquery)
Also I don't understand the Future instead of List. If anyone would shed some light on those that would help.
I am not 100% sure how to achieve what you need using LINQ so to give you an option I am just putting up an alternative solution using nHibernate Criteria (this will execute in one database hit):
// Create a query
ICriteria query = Session.CreateCriteria<WorkShopItem>("wsi");
// Restrict to items due within the next 14 days
query.Add(Restrictions.Le("DateDue", DateTime.Now.AddDays(14));
// Return all TaskNames from Todo's
DetachedCriteria allTodos = DetachedCriteria.For(typeof(Todo)).SetProjection(Projections.Property("TaskName"));
// Filter Work Shop Items for any that do not have a To-do item
query.Add(SubQueries.PropertyNotIn("Name", allTodos);
// Return results
var matchingItems = query.Future<WorkShopItem>().ToList()
I'd recommend
var workshopItemsDueSoon = Session.QueryOver<WorkshopItem>()
.Where(w => w.DateDue <= twoWeeksTime)
var allTodos = Session.QueryOver<ToDo>();
Instead of
var allTodos = Session.QueryOver<ToDo>().List();
var workshopItemsDueSoon = Session.QueryOver<WorkshopItem>()
.Where(w => w.DateDue <= twoWeeksTime).List();
So that the collection isn't iterated until you need it to be.
I've found that it's helpfull to use linq extension methods to make subqueries more readable and less awkward.
For example:
var matches = from wsi in workshopItemsDueSoon
where !allTodos.Select(it=>it.TaskName).Contains(wsi.Name)
select wsi
Personally, since the query is fairly simple, I'd prefer to do it like so:
var matches = workshopItemsDueSoon.Where(wsi => !allTodos.Select(it => it.TaskName).Contains(wsi.Name))
The latter seems less verbose to me.
I have a LINQ query which contains a method GetInstanceForDatabase()
principlesList.Select(p => p.GetInstanceForDatabase()).ToList()
where
List<PrincipleInstance>() principlesList = ...
// (contains list of principle like "Manual Trades", "OPM", "Flora")
GetInstanceForDatabase() is a method which takes all other info about a principle (like manual trades).
My problem is that I want to sort out only principle like only "Manual Trades".
I want to put a where clause. I tried but it is fails.
To get a single item use:
query.First(x => x.property == "Manual Trades");
// or
query.FirstOrDefault(x => x.property == "Manual Trades");
var list = p.GetInstanceForDatabase().where(x => x.propertyName == "Manual Trades").ToList();
I'm sure you're GetInstanceForDatabase needs to return your collection that you then filter for the 'Manual Trades' but I can't really tell how you get your list of PrincipalInstances from the question.
This is the correct syntax of using Where in LINQ
principlesList.Select(p => p.GetInstanceForDatabase()).Where(p => p.SomeProperty == "SomeValue").ToList();