In need a query that will help me solve this.
Here's my table 'tags':
id (int)
name (String)
user_id (int)
hardware_id (int)
I am grouping the results of the 'tags' table by hardware_id. I also have a List of tags (List<string>).
I want to get the hardware Id of the groups that all of the tags in the custom List matches at a name in the table above.
In other words, I want to get the hardware_id's that the custom List tags matches their name's. There might be name's that doesn't have a match in the custom list, but all of the custom list tags, must be in the group, and if it satisfies this need, I can the Id of that group.
I found it hard to explain and I didn't get an answer for that. I thought about doing it with foreach because it was so hard to solve, but I couldn't do it either and it's very inefficient to do it that way.
Example:
List : ['tag1', 'tag2']
Table Rows:
1, tag1, 5, 1
2, tag2, 5, 1
3, tag3, 5, 1
4, tag4, 5, 2
5, tag5, 6, 2
In this case, I should get the hardware_id of 1, because although one of the hardware Id's have tag3, it doesn't have any rows with a tag name that isn't in the List. IF the List had 'tag4', the hardware_id = 1 WOULDN'T be returned, because the List has a tag that the hardware_id group doesn't have.
If the Group doesn't have an item that the List has, it won't appear in the final result.
Someone game me this code, but it didn't work:
List<decimal> matchingHardareIds = db.tags.GroupBy(x => x.hardware_id)
.Where(x => x.All(s => tags.Contains(s.name.ToLower()) || 0 == tags.Count() && (s.user_id == userId)))
.Select(x => x.Key).ToList();
In that query, when I have one tag in the List and in the table I have several items with hardware_id 1 and one of them has a 'name' that is equal to the value in the List it will return empty results. this is because the rows in the table for a specific group by hardware_id, has a row with a name that doesn't appear in the custom List.
I need a query in either Entity Framework or Linq. Thanks a lot.
Use this:
var t = db.tags.GroupBy(x => x.hardware_Id)
.Where(x => tags.All(y =>
x.Any(z=> z.name == y)))
.Select(x=>x.Key).ToList();
Can not provide you with the entity framework or linq query, but the sql solution is to count the matches like this:
SELECT hardware_id
FROM tags
WHERE name IN (<list>)
GROUP BY hardware_id
HAVING COUNT(DISTINCT name) = <listDistinctCount>
<listDistinctCount> is the count of distinct values in the list. Which you can prepare prior to the query.
Related
I'm running a query that will get results based on a location search and date. I have a geography column with location points (lat/long) that's indexed. When I search for an event on a date it searches for all events within a distance (radius) on that date.
The problem is that if there are, say 10 events, all at the same location on the same date, all 10 results will come back in the first page. I'd like to mix this up and only show 2-3 from each location to give the result set some variety, so the user doesn't just see all events from one location.
I know I can use distinct to only fetch one event from each location, but how would I use it to get me 2-3 distinct values?
Here is my query so far.
viewModel.Events = dbContext.YogaSpaceEvents
.Where(i => i.EventDateTime >= adjustedSearchDate &&
i.LocationPoints.Distance(location) <= radius)
.Distinct()
.OrderBy(i => i.EventDateTime)
.Select(i => new EventResult
{
//fill view model here
})
.ToPagedList(Page, 10);
I don't think there's a way to get EF to generate such a query, which for SQL Server would be something like this:
with q as
(
select *,
( row_number() over (partition by StateProvinceId order by CityID) -1 ) / 3 MyRanking
from Application.Cities
)
select CityId, CityName,StateProvinceID
from q
order by MyRanking, StateProvinceID, CityID
offset 10 rows
fetch next 20 rows only
Note that this example doesn't use distance. But the idea is identical: the first 3 cities in each state are returned first, then the next 3, etc.
Or you could fetch all the matching events and sort them in memory.
I think you should be able to do something like:
dbContext.YogaSpaceEvents
.Where(i => i.EventDateTime >= adjustedSearchDate &&
i.LocationPoints.Distance(location) <= radius)
.GroupBy(i => i.Geography)
.SelectMany(g => g.OrderBy(x => x.EventDateTime).Take(3))
.Select(i => new EventResult { //fill view model here })
.ToPagedList(Page, 10);
I have a survey where users can post answers and since the answers are being saved in the db as a foreign key for each question, I'd like to know which answer got the highest rating.
So if the DB looks somewhat like this:
answer_id
1
1
2
how can I find that the answer with an id of 1 was selected more times than the one with an id of 2 ?
EDIT
So far I've done this:
#question = AnswerContainer.where(user_id: params[:user_id]) which lists the things a given user has voted for, but, obviously, that's not what I need.
you could try:
YourModel.group(:answer_id).count
for your example return something like: {1 => 2, 2 => 1}
You can do group by and then sort
Select answer_id, count(*) as maxsel
From poll
Group by answer_id
Order by maxsel desc
As stated in rails documentation (http://api.rubyonrails.org/classes/ActiveRecord/Calculations.html) when you use group with count, active record "returns a Hash whose keys represent the aggregated column, and the values are the respective amounts"
Person.group(:city).count
# => { 'Rome' => 5, 'Paris' => 3 }
I need some help creating an LINQ select, i have a table with some columns in it, but only 2 of interest to this problem.
userid, type
Now this table have many thousands entries, and I only want the top, let’s say 50. So far so good, but the hard part is that there a lot of rows in success that should only be counted as 1.
Example
Type UserId
============
Add 1
Add 1
Add 1
Add 2
I would like this to only be counted as 2 in the limit of rows I am taking out, but I would like all the rows to be outputted still.
Is this possible with a single SQL request, or should I find another way to do this?
Edit: I can add columns to the table, with values if this would solve the problem.
Edit2: Sotred procedures are also an solution
Example 2: This should be counted as 3 rows
Type UserId
============
Add 1
Add 1
Add 2
Add 1
Are you stuck on LINQ?
Add a PK identity.
Order by PK.
Use a DataReader and just count the changes.
Then just stop when the changes count is at your max.
If you are not in a .NET environment then same thing with a cursor.
Since LINQ is deferred you might be able to just order in LINQ and then on a ForEach just exit.
I'm not close to a computer right now so I'm not sure is 100% correct syntax wise, but I believe you're looking for something like this:
data.Select(x => new {x.Type, x.UserId})
.GroupBy(x => x.UserId)
.Take(50);
You could do it with Linq, but it may be a LOT slower than a traditional for loop. One way would be:
data.Where((s, i) => i == 0 ||
!(s.Type == data[i-1].Type && s.UserId == data[i-1].UserId))
That would skip any "duplicate" items that have the same Type and UserID as the "previous" item.
However this ONLY works if data has an indexer (an array or something that implements IList). An IEnumerable or IQueryable would not work. Also, it is almost certainly not translatable to SQL so you'd have to pull ALL of the results and filter in-memory.
If you want to do it in SQL I would try either scanning a cursor and filling a temp table if one of the values change or using a common table expression that included a ROW_NUMBER column, then doing a look-back sub-query similar to the Linq method above:
WITH base AS
(
SELECT
Type,
UserId,
ROW_NUMBER() OVER (ORDER BY ??? ) AS RowNum
FROM Table
)
SELECT b1.Type, b1.UserId
FROM base b1
LEFT JOIN base b2 ON b1.RowNum = b2.RowNum - 1
WHERE (b1.Type <> b2.Type OR b1.UserId <> b2.UserId)
ORDER BY b1.RowNum
You can do this with LINQ, but I think it might be easier to go the "for(each) loop" route...
data.Select((x, i) => new { x.Type, x.UserId, i })
.GroupBy(x => x.Type)
.Select(g => new
{
Type = g.Key,
Items = g
.Select((x, j) => new { x.UserId, i = x.i - j })
})
.SelectMany(g => g.Select(x => new { g.Type, x.UserId, x.i }))
.GroupBy(x => new { x.Type, x.i })
.Take(50);
.SelectMany(g => g.Select(x => new { x.Type, x.UserId }));
I have a model called Shops with an attribute called brands, brands is a text field and contains multiple brands. What i would like to do is select all unique brands and display them sorted in alphabetic order
#brands = Shop.all(:select => 'distinct(brands)')
What to do from here?
If Shop#brands can hold multiple values like for example: "rony, hoke, fike", then I can reluctantly suggest doing something like this:
#brands = Shop.all(:select => 'brands').each { |s|
s.brands.split(',').map { |b|
b.strip.downcase
}
}.flatten.uniq.sort
BUT, you should really think about your data model here to prevent such hackery. You couuld break out the brands into it's own table + model and do a many to many relationship with Shop.
I have an Article with a Set of Category.
How can I query, using the criteria interface, for all Articles that contain all Categories with a certain Id?
This is not an "in", I need exclusively those who have all necessary categories - and others. Partial matches should not come in there.
Currently my code is failing with this desperate attempt:
var c = session.CreateCriteria<Article>("a");
if (categoryKeys.HasItems())
{
c.CreateAlias("a.Categories", "c");
foreach (var key in categoryKeys)
c.Add(Restrictions.Eq("c", key)); //bogus, I know!
}
Use the "IN" restriction, but supplement to ensure that the number of category matches is equal to the count of all the categories you're looking for to make sure that all the categories are matched and not just a subset.
For an example of what I mean, you might want to take a look at this page, especially the "Intersection" query under the "Toxi solution" heading. Replace "bookmarks" with "articles" and "tags" with "categories" to map that back to your specific problem. Here's the SQL that they show there:
SELECT b.*
FROM tagmap bt, bookmark b, tag t
WHERE bt.tag_id = t.tag_id
AND (t.name IN ('bookmark', 'webservice', 'semweb'))
AND b.id = bt.bookmark_id
GROUP BY b.id
HAVING COUNT( b.id )=3
I believe you can also represent this using a subquery that may be easier to represent with the Criteria API
SELECT Article.Id
FROM Article
INNER JOIN (
SELECT ArticleId, count(*) AS MatchingCategories
FROM ArticleCategoryMap
WHERE CategoryId IN (<list of category ids>)
GROUP BY ArticleId
) subquery ON subquery.ArticleId = EntityTable.Id
WHERE subquery.MatchingCategories = <number of category ids in list>
I'm not 100% sure, but I think query by example may be what you want.
Assuming that Article to Category is a one-to-many relationship and that the Category has a many-to-one property called Article here is a VERY dirty way of doing this (I am really not proud of this but it works)
List<long> catkeys = new List<long>() { 4, 5, 6, 7 };
if (catkeys.Count == 0)
return;
var cr = Session.CreateCriteria<Article>("article")
.CreateCriteria("Categories", "cat0")
.Add(Restrictions.Eq("cat0.Id", catkeys[0]));
if (catkeys.Count > 1)
{
for (int i = 1; i < catkeys.Count; i++)
{
cr = cr.CreateCriteria("Article", "a" + i)
.CreateCriteria("Categories", "cat" + i)
.Add(Restrictions.Eq("cat" + i + ".Id", catkeys[i]));
}
}
var results = cr.List<Article>();
What it does is to re-join the relationship over and over again guaranteeing you the AND between category Ids. It should be very slow query especially if the list of Ids gets big.
I am offering this solution as NOT a recommended way but at least you can have something working while looking for a proper one.