I have two tables, one contains entities other entitylog.
MyEntity:
id, lat, lon
A entity has a position in the world.
MyEntityLog:
id, otherid, otherlat, otherlon
Entity with id has interacted with otherid at otherid's latitude and longitude.
For instance, I have the following entities:
1, 4.456, 2.234
2, 3.344, 6.453
3, 6.234, 9.324
(not very accurate, but it serves the purpose).
Now, If entity 1 interact with 2 the result on the log table would look like:
1, 2, 3.344, 6.453
So my question is, how can I for listing entity 1's available interactions NOT include the ones on the log table?
The result of listing entity 1's available interactions should be only be entity 3 as it already has a interaction with 2.
First make a list of ids that interact with entity 1:
var id1 = 1;
var excluded = from l in db.EntityLogs
where l.id == id1
select l.otherid;
then find the entries not having an id in this list or equal to id1:
var logs= from l in db.EntityLogs
where !excluded.Contains(l.id) && l.id != id1
select l;
Note that linq will defer the execution of excluded and incorporate it in the execution of logs.
Not sure if I understand your question, I guess I need more details, but if you want to list the entities that have no entry in log table, one solution will be something like this, assuming myEntities is the collection of MyEntity and myEntityLogs is the collection of MyEntityLog
var firstList = myEntities.Join(myEntityLogs, a => a.Id, b => b.Id, (a, b) => a).Distinct();
var secondList = myEntities.Join(myEntityLogs, a => a.Id, b => b.OtherId, (a, b) => a).Distinct();
var result = myEntities.Except(firstList.Concat(secondList)).ToList();
Related
Let’s assume I have three tables in my database:
Authors(PK Id, AuthorName)
Books(PK Id, BookName)
Authors_Books(FK BookId, FK AuthorId)
I need to write a method which passes in a parameter int[] authorsIds and returns all books (Id, BookName, list of authors of this book) if it was written by any author whose Id contains in int[] authorsIds parameter.
I need LINQ query (query method).
I really need a help. Appreciate your help very much.
var int[] authors = { 1, 2, 3 };
var books = from book in books
where book.Authors.Any(x => authors.Contains(x.AuthorId))
select book;
PS: I assume book.Authors is your reference to Authors_Books table (or maybe has a different name).
this answer is based on the exact structure without considering that A obj has B in its structure
var book = from b in books
where book.Id in ( from ab in AuthersBooks
where selectedAuthers.contains(ab.AutherId)
select ab.bookId ) //now we have books that are authered by one of the selected authers
select new { BookId = b.Id, // now we create an anonymos object to contain any info we need
BookName = b.Name,
BookAuthers = (from a in authers
join ab in AuthersBooks
on a.Id == ab.AuthersId
where ab.bookid == b.Id
select a)
this will propably have syntax errors and after correcting you may get an error about multiple threads which already has an answer here
I guess there must be an easy way, but not finding it. I would like to check whether a list of items, appear (completely or partially) in another list.
For example: Let's say I have people in a department as List 1. Then I have a list of sports with a list of participants in that sport.
Now I want to count, in how many sports does all the people of a department appear.
(I know some tables might not make sense when looking at it from a normalisation angle, but it is easier this way than to try and explain my real tables)
So I have something like this:
var peopleInDepartment = from d in Department_Members
group d by r.DepartmentID into g
select new
{
DepartmentID = g.Key,
TeamMembers = g.Select(r => d.PersonID).ToList()
};
var peopleInTeam = from s in Sports
select new
{
SportID = s.SportID,
PeopleInSport = s.Participants.Select(x => x.PersonID),
NoOfMatches = peopleInDepartment.Contains(s.Participants.Select(x => x.PersonID)).Count()
};
The error here is that peopleInDepartment does not contain a definition for 'Contains'. Think I'm just in need of a new angle to look at this.
As the end result I would like print:
Department 1 : The Department participates in 3 sports
Department 2 : The Department participates in 0 sports
etc.
Judging from the expected result, you should base the query on Department table like the first query. Maybe just include the sports count in the first query like so :
var peopleInDepartment =
from d in Department_Members
group d by r.DepartmentID into g
select new
{
DepartmentID = g.Key,
TeamMembers = g.Select(r => d.PersonID).ToList(),
NumberOfSports = Sports.Count(s => s.Participants
.Any(p => g.Select(r => r.PersonID)
.Contains(p.PersonID)
)
)
};
NumberOfSports should contains count of sports, where any of its participant is listed as member of current department (g.Select(r => r.PersonID).Contains(p.PersonID))).
I'm porting some sql stored procedure logic, which would return multiple tables in a dataset, to entity framework strongly typed objects, queried with linq.
Basically I need the data from tables A, B, and C, where C has a foreign key to B, and B has a foreign key to A. But I don't want every C with a FK to B, just the C's with a certain constraint X.
So basically, the stored proc basically said
TableA = select from A where A.AID = AIDPassedIn
TableB = select from B where B.AID = AIDPassedIn
TableC = select from TableB where TableB.XID = XIDPassedIn
return new DataSet(TableA, TableB, TableC);
//yes this is gross and confusing, thus our current efforts
Entity framework almost makes this super easy like so
A.Include("B.C").Where(a => a.AID == AIDPassedIn)
My only problem is that this doesn't include constraint X on the C table. I've read a bunch of articles, but everything I've read suggests things I could add to the where clause, and that would filter what A objects I end up with. I should only end up with one A object though, regardless of the properties of it's children. What I want is The A with AIDPassedIn, and all it's child B's, and all the B's children C that match constraint X.
I feel like this is one of my worst phrased questions ever but I'm at a bit of a block. Any help would be great thanks!
You can try it along the lines of the following:
var AList = context.As.Where(a => a.AID == AIDPassedIn)
.Select(a => new
{
A = a,
Bs = a.Bs,
Cs = a.Bs.Select(b => b.Cs.Where(c => c.XID == XIDPassedIn))
})
.AsEnumerable()
.Select(x => x.A)
.ToList(); // or SingleOrDefault if AIDPassedIn is the PK
Entity Framework will put the object graph together automatically (even without using Include) as long as you don't disable change tracking.
Here a sample dataset:
OrderProduct is a table that contains the productIds that were part of a given order.
Note: OrderProduct is a database table and I am using EF.
OrderId, ProductId
1, 1
2, 2
3, 4
3, 5
4, 5
4, 2
5, 2
5, 3
What I want to be able to do is find an order that contains only the productIds that I am searching for. So if my input was productIds 2,3, then I should get back OrderId 5.
I know how I can group data, but I am unsure of how to perform the select on the group.
Here is what I have:
var q = from op in OrderProduct
group op by op.OrderId into orderGroup
select orderGroup;
Not sure how to proceed from here
IEnumerable<int> products = new List<int> {2, 3};
IEnumerable<OrderProduct> orderProducts = new List<OrderProduct>
{
new OrderProduct(1, 1),
new OrderProduct(2, 2),
new OrderProduct(3, 4),
new OrderProduct(3, 5),
new OrderProduct(4, 5),
new OrderProduct(4, 2),
new OrderProduct(5, 2),
new OrderProduct(5, 3),
};
var orders =
(from op in orderProducts
group op by op.OrderId into orderGroup
//magic goes there
where !products.Except(orderGroup.Select(x => x.ProductId)).Any()
select orderGroup);
//outputs 5
orders.Select(x => x.Key).ToList().ForEach(Console.WriteLine);
Or you can have another version as pointed in another answer, just replace
where !products.Except(orderGroup.Select(x => x.ProductId)).Any()
on
where products.All(pid => orderGroup.Any(op => op.ProductId == pid))
second one will have ~ 15% better performance (I've checked that)
Edit
According to the last requirement change, that you need orders that contain not all productIds you are searching, but exactly those and only those productIds, I wrote an updated version:
var orders =
(from op in orderProducts
group op by op.OrderId into orderGroup
//this line was added
where orderGroup.Count() == products.Count()
where !products.Except(orderGroup.Select(x => x.ProductId)).Any()
select orderGroup);
So the only thing you'll need is to add a precondition ensuring that collections contains the same amount of elements, it will work for both previous queries, and as a bonus I suggest 3rd version of the most important where condition:
where orderGroup.Select(x => x.ProductId).Intersect(products).Count() == orderGroup.Count()
At first glance, I'd try something like this:
var prodIds = new[] {2, 3};
from o in context.Orders
where prodIds.All(pid => o.OrderProducts.Any(op => op.ProductId == pid))
select o
In plain language: "get the orders that have a product with every ID in the given list."
Update
Since it appears you are using LINQ to SQL rather than LINQ to Entities, here's another approach:
var q = context.Orders;
foreach(var pid in prodIds)
{
q = q.Where(o => o.OrderProducts.Any(op => op.ProductId == pid));
}
Rather than using a single LINQ statement, you essentially build the query piecemeal.
Thanks to StriplingWarrior's answer I managed to figure this out. Not sure if this is the best way to do this, but it works.
List<int> prodIds = new List<int>{2,3};
var q = from o in Orders
//get all orderproducts that contain products in the ProdId list
where o.OrderProducts.All(op => prodIds.Contains(op.ProductId))
//now group the OrderProducts by the Orders
select from op in o.OrderProducts
group op by op.OrderId into opGroup
//select only those groups that have the same count as the prodId list
where opGroup.Count() == prodIds.Count()
select opGroup;
//get rid of any groups that may be empty
q = q.Where(fi => fi.Count()> 0);
(I am using LinqPad, which is why the query looks a little funky - no context, etc)
Suppose I have 3 tables: A(aid, ...), B(bid, ...) Relationship(aid, bid, ...)
Then I have a aid as parameter, I want to get the result from b. If use SQL, will be like
select b.* from B join Relationship on b.bid = Relationship.bid
where relationship.aid = aid_param
how to write linq with same result as above SQL. (the foreign key was not created correctly in this case)?
Assuming that you've used the designer to add your tables to the LINQ data context and you have either foreign key relationships defined in the database or have hand-coded the associations in the designer, you should simply be able to reference the B table and it's EntitySet of Relationship properties, filtered by your parameter, and check if there are any matches.
var relationships = db.B.Any( b => b.Relationships.Where( r => r.aid == aid_param ) );
var bQuery = from r in MyContext.Relationship
where r.aid == aid_param
select r.B;
If you don't have a relationship set in the model, then u can:
var bQuery = from b in myContext.B
where myContext.Relationship
.Any( r => r.aid == aid_param && b.bid == r.bid)
select b;
var output =
from b
from Relationship
where (b.bid = Relationship.bid,
relationship.aid = aid_param)