I'm trying to retrieve records ordered by a DateTime with Linq to entities, but I need them as distinct records as well.
My table design looks like this:
Where blogItemNodeId is an Umbraco CMS node (the blog item node to which a comment can be created)
The requirement is that a list of blog items can be sorted by how many comments they have. So I need to get the latest comments distinct by blogItemNodeId to display those blog items.
My current linq query looks like this:
var distinctComments = (from c in ctx.BlogComments
orderby c.date
group c by c.blogItemNodeId
into uniqueRecords
select uniqueRecords.FirstOrDefault());
The problem with this query is that it finds the first (hence FirstOrDefault()) record with distinct blogItemNodeId where it should find the one which is newest of all comments with the same blogItemNodeId.
Does anyone know how to achieve this? :-)
Thanks a lot in advance.
EDIT
I managed to get it to work by doing this:
var allComments = (from c in ctx.BlogComments
orderby c.date descending
select c).ToList();
var distinctComments = allComments.GroupBy(x => x.blogItemNodeId).Select(y => y.FirstOrDefault());
But then I have to get all the comments before doing the group which is not very elegant nor performant.
Any help is greatly appreciated!
You could combine both the orderBy statement and the GroupBy statement into one single statement like this:
var distinctComments = ctx.BlogComments.OrderBy(c => c.date)
.GroupBy(x => x.blogItemNodeId)
.Select(y => y.FirstOrDefault());
If the performance is bad, you could cache your DataContext in the HttpCache through a Singleton. See this blogpost for an example. This is based on the Umbraco DataContext but can be easily modified for use with another type of context.
Related
How can I make a model join query(condition) and sort on relation models on Sails?
Example: I have 4 tables(collections in mongodb) and 4 related models in mongodb:
User: user_id, name
Follow: user_id, following_id (user id is being followed)
Point: user_id, point
Post: name, content, user_id, created_at
So from the post table, I want to make a query to find the posts of users that I'm following and sort by their point. Like this raw sql:
SELECT post.* FROM post
LEFT JOIN user_point up ON up.user_id = post.user_id
WHERE post.user_id IN (1,2,3,4) // assume I got my following_user_ids result is 1,2,3,4 for this case so no need to join follow table
ORDER BY up.point DESC // high point then first return
I don't know how can do this by Sails model? I have read many instructions by got no helps. Almost people said: Sails Association, but it just helps return the relation instead of do the where or order by to sort original model results(is this case: post).
I have worked with Yii2, a PHP framework so with this case I can do it easily:
Post::model()->leftJoin('user_point up', 'up.user_id = post.user_id')->where(['post.user_id' => [1,2,3,4])->orderBy(['up.point' => SORT_DESC])->all();
I'm stucked in Sails, very thanks if someone help me!!!
Because you're using Mongo, and because you need the full power of normal JOIN's, you will probably be forced to use some other ORM solution (i.e. mongodb package on npm) for queries like that.
Why? See the API documentation for sendNativeQuery(), which states native query features are only available for SQL-like DBMS's.
I have made an Xamarin forms application and the problem that I have a list named lista2 which has an object named poli. Poli is the city that it is located. I want to make a list based on distinct cities, which i have done using this command
var poleislist = lista2.Select(x => x.poli).Distinct();
now I want this poleislist to be sorted based on the amount of times that each element is on the lista2. For example the bigger cities appear more often and I want them in the first places of the list because this list(poleislist) is going to be the itemsource of a picker.
Thank you very much!
Instead of using Distinct you could Group the list, sort it by count descending then Select the poli.
It would be something like this:
var poleislist = lista2.GroupBy(item => item.poli)
.OrderByDescending(a => a.Count())
.Select(x => x.Key)
.ToList();
Note: sorry did not get to test it but this should work. Basically this should get you all the cities in the list, ordered descending by the number of times it appears.
Hope this helps.-
I have been struggling for some time now and I can't really find anyone having done the same thing before.
I'm creating a backend module in TYPO3 7.6 which belongs to a shop extension.
The shop extension with the backend module was created with the extension builder. The shop has the following three models:
Product (products which can be ordered through the shop)
Productsorder (link to the customer)
ProductsorderPosition (the ordered product, the ordered amount and size and the link to the Productsorder)
The customers are of a model type from a different extension. These customers are linked to fe_users.
Now what I wanna do in my backend module is getting an overview to all these orders listed with the customer, some information about the fe_user and of course the product. I have created a sql-query, which does exactly that:
SELECT p.productname, p.productpriceperpiece,
pop.amount, pop.size,
h.name, h.address, h.zipcode, h.city, h.email, h.phone,
f.first_name, f.last_name, f.email
FROM `tx_gipdshop_domain_model_productorderposition` AS pop
JOIN `tx_gipdshop_domain_model_product` AS p ON pop.products = p.uid
JOIN `tx_gipdshop_domain_model_productsorder` AS po ON pop.productorder = po.uid
JOIN `tx_gipleasedisturbhotels_domain_model_hotel` AS h ON po.hotel = h.uid
JOIN `fe_users` AS f ON h.feuser = f.uid
If I use this query from the product repository it gives back the right amount of data records but they're of type product and the products are all "empty" (uid = 0 etc).
I've added an additional action for this in the product controller (getOrdersAction) and in the repository containing the query I've added a method findAllOrders.
I'm still rather a beginner in TYPO3 but I can somehow understand why it returns data sets of type Product when the query is called from the ProductRepository. But what I do not know is how I can get all the information from the query above and list it in the backend module.
I've already thought about moving the query to the ProductsorderPositionRepository but I would probably be faced with a similar problem, it would only return the information from the ProductsorderPosition and everything else would be left out.
Can someone point me to the right direction?
Would I need to create another model with separate repository and controller? Isn't there an easier way?
If you need more information, just ask! ;)
First of all, you are doing a joined query with subsets of data mixed from multiple tables. There is nothing against this.
Because of this, there is no "model" which has the mixed datasets.
If you are using the default query thing in a repository, the magic behind the repository assumes that the result of the query statement reflects the defined base model for this repository.
Moving the query function to another repository does not solve the problem.
You have not provided the code snippet you are executing the sql statement, so I assume you have used the query thing in the repository to execute the statement. Something like this:
$result = $query->statement('
SELECT p.productname, p.productpriceperpiece,
pop.amount, pop.size,
h.name, h.address, h.zipcode, h.city, h.email, h.phone,
f.first_name, f.last_name, f.email
FROM `tx_gipdshop_domain_model_productorderposition` AS pop
JOIN `tx_gipdshop_domain_model_product` AS p ON pop.products = p.uid
JOIN `tx_gipdshop_domain_model_productsorder` AS po ON pop.productorder = po.uid
JOIN `tx_gipleasedisturbhotels_domain_model_hotel` AS h ON po.hotel = h.uid
JOIN `fe_users` AS f ON h.feuser = f.uid', NULL);
or have used the query building stuff.
First solution
The first and simpliest solution would be to retrieve the result as plain php array. Before TYPO3 7.0 you could have done this by using this:
$query->getQuerySettings()->setReturnRawQueryResult(TRUE);
With TYPO3 7.0 this deprecated method was removed from the core.
The only way is to define the query and call $query->execute(TRUE); for now.
This should return the data in pure array form.
This is the simpliest one, but as we are in the extbase context this should not be suffering enough.
Second Solution - no, just an idea that I would try next
The second solution means that you have some work to do and is for now only a suggestion, because I have not tried this by myself.
Create a model with the properties and getter/setters for the result columns of your query
Create a corresponding repository
Third solution
Not nice, but if nothing else works, fall back to the old TYPO3 v4 query methods:
$GLOBALS['TYPO3_DB']->exec_SELECTgetRows([...]))
and replace this with the QueryBuilder in/for TYPO3 v8.
This is really not nice.
I hope I could direct you to the right way, even if not giving a full solving solution.
I am trying to execute a DQL (Doctrine) query that retrieve the latest answers of different doctors.
we have table answer, member, Location (doctor table) and many other table connected to the doctor information. However I want to get the latest answer but the condition is one answer for a doctor. I do some search and know something about group by and order by dont work together !
Here is the query in DQL:
$query = Doctrine_Query::create()
->select("a.answer_id as answer_id,m.member_is as member_id,a.member_id")
->from('Answer a')
->leftJoin('a.Member m on m.member_id = a.member_id')
->orderBy('a.date_added DESC')
->groupBy('m.member_id')
->limit(5);
but this query return undesirable results. Can anyone tell me where is the mistake?
Unfortunately you need to perform a subquery for that, which according to this question, DQL does not support. However in that question it's suggested that you send a native query.
i am wondering how can i select specific number of child objects instead of taking them all with include?
lets say i have object 'Group' and i need to select last ten students that joined the group.
When i use '.Include("Students"), EF includes all students. I was trying to use Take(10), but i am pretty new to EF and programming as well, so i couldn't figure it out.
Any suggestions?
UPDATED:
ok, i have Group object already retrieved from db like this:
Group group = db.Groups.FirstOrDefault(x=>x.GroupId == id)
I know that i can add Include("Students") statement, but that would bring ALL students, and their number could be quite big whether i need only freshest 10 students. Can i do something like this: var groupWithStudents = group.Students.OrderByDescending(//...).Take(10);?
The problem with this is that Take<> no longer appears in intellisense. Is this clear enough? Thanks for responses
I believe Take(10) would be correct.
var Students= (from c in Groups
orderby c.DateAdded descending
select c).Take(10);
My experience with Take though is that it generates some awful sql.
EDIT:
see if this blog post helps, it talks of conditional includes.
http://blogs.msdn.com/b/alexj/archive/2009/10/13/tip-37-how-to-do-a-conditional-include.aspx
Couldn't make Gratzy's suggestion with conditional include work... and found the solution here: http://msdn.microsoft.com/en-us/library/bb896249.aspx
Query would look like this:
group.Students.Attach(group.Students
.CreateSourceQuery()
.OrderByDescending(x=>x.JoinDate)
.Take(10));
This is exactly what i was looking for!
Thanks for all responses anyway!