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I have many to many relationship, table Product, table Category and join table ProductCategory.
I need to convert this SQL query to LINQ C#:
Select TOP 3 Categories.id, Categories.Description, avg(Products.Price) as MeanPrice, count(Products.IsAvailable) as NumberOfAvailableProducts
FROM Categories
INNER JOIN ProductCategories on Categories.Id =
ProductCategories.CategoryId
INNER JOIN Products on Products.Id = ProductCategories.CategoryId
WHERE Products.IsAvailable='true'
GROUP BY Categories.Id, Categories.Description
ORDER BY MeanPrice DESC
I would appreciate help, thanks.
There are so many examples in the Internet for you to start learning how to write LINQ effectively (including the post from NetMage above).
But I would give you the examples anyway, based on your case above, with an assumption that this T-SQL of yours :
INNER JOIN Products on Products.Id = ProductCategories.CategoryId
might've been a typo, because what you really meant was maybe like this :
INNER JOIN Products on Products.Id = ProductCategories.ProductId
So, this is the snippet when you ask me how could I do that in LINQ :
var query = (from finalq in
(
from cat in categories
join procat in
// Join [ProductCategories] with [Products] first
(
from pc in productcategories
join p in products on pc.ProductId equals p.Id
where p.IsAvailable == "True"
select new
{
CategoryId = pc.CategoryId,
ProductId = p.Id,
ProductPrice = p.Price
}
)
// And then join the result with [Categories]
on cat.Id equals procat.CategoryId
select new
{
CategoryId = cat.Id,
CategoryDescription = cat.Description,
ProductPrice = procat.ProductPrice
}
)
// Then aggregate it to get the final result
group finalq by new { finalq.CategoryId, finalq.CategoryDescription } into finalGroup
orderby finalGroup.Average(c => c.ProductPrice) descending
select new
{
CategoryId = finalGroup.Key.CategoryId,
CategoryDescription = finalGroup.Key.CategoryDescription,
ProductPrice = finalGroup.Average(c => c.ProductPrice),
NumberOfAvailableProducts = finalGroup.Count()
}
)
// And take the TOP 3 rows (I know it's ugly but I don't have a choice)
.Take(3);
So, that's it. I hope you can get something from my post here, and later may create your own, a better version of this quick example.
Good luck!
For translating SQL to LINQ query comprehension:
Translate FROM subselects as separately declared variables.
Translate each clause in LINQ clause order, translating monadic operators (DISTINCT, TOP, etc) into functions applied to the whole LINQ query.
Use table aliases as range variables. Use column aliases as anonymous type field names.
Use anonymous types (new { ... }) for multiple columns.
Left Join is simulated by using a into join_variable and doing another from from the join variable followed by .DefaultIfEmpty().
Replace COALESCE with the conditional operator and a null test.
Translate IN to .Contains() and NOT IN to !...Contains()
SELECT * must be replaced with select range_variable or for joins, an anonymous object containing all the range variables.
SELECT fields must be replaced with select new { ... } creating an anonymous object with all the desired fields or expressions.
Proper FULL OUTER JOIN must be handled with an extension method.
Related
I have a SQL query that basically joins the MyWords table to the MyTranslations table on two keys. Here are my tables for better understanding.
MyWords table:
Id
WordString
LangType
MyTranslations table:
Id
WordColumnAId
WordColumnBId
Please note that WordColumnAIdand WordColumnBId columns are FKs that represents the MyWords.Id.
My SQL query:
SELECT MyTranslations.Id
,WordColumnAId
,WordColumnBId
,MyWords.WordString
,MyWords.LangType
FROM MyTranslations
join MyWords on (MyTranslations.WordColumnAId = MyWords.Id or MyTranslations.WordColumnBId = MyWords.Id)
where MyWords.LangType !=#currentLangType
I know it doesn't make sense to use join on with multiple keys at first glance but I'm trying to a cross-query that would join two tables whether the key is on WordColumnAId or WordColumnBId.
Problem
I'm trying to adapt the above T-SQL query into a LinQ query. The problem is that I can't find my way around LinQ to use two keys in a single join query.
Here's what I've got so far:
from translation in queryableTranslation
join word in _myWordRepository on translation.WordColumnAId equals word.Id // This is where I want to add `or translation.WordColumnBId equals word.Id` but get errors.
where word.LangType != currentLangType
select new QueryResultDto {
MyTranslationId = translation.Id,
WordString = word.WordString,
LanguageType = word.LangType,
WordColumnAId = translation.WordColumnAId,
WordColumnbId=translation.WordColumnbId,
};
I'm very new to the LinQ and trying to learn.
So my question: is there a way to achieve this in LinQ or am I trying the impossible? I'm also open to better approaches.
EF and other LINQ providers should translate query to INNER JOIN when using this syntax:
var query =
from translation in queryableTranslation
from word in _myWordRepository.Where(word => translation.WordColumnAId == word.Id
|| translation.WordColumnBId = word.Id)
where word.LangType != currentLangType
select new QueryResultDto
{
MyTranslationId = translation.Id,
WordString = word.WordString,
LanguageType = word.LangType,
WordColumnAId = translation.WordColumnAId,
WordColumnbId=translation.WordColumnbId,
};
I'm a junior developer and trying to convert the following linq statement to T-SQL:
var items = from u in DataContext.Users_SearchUsers(searchPara.UserFirstName,
searchPara.UserLastName,
searchPara.UserEmailAddress,
fetchOptions.page,
fetchOptions.rp,
fetchOptions.sortname,
fetchOptions.sortorder)
.ToList()
join a in DataContext.UserAccesses
.Where(x => x.Access.AccessTypeId == 4).ToList() on u.UserID equals a.UserId into accessGroup
select new {};
Can one please help me ? into accessGroup ---> (very important)
First of all you need to understand where your data is coming from. You are loading information from Users_SearchUsers on the one hand and UserAccesses on the other hand. The first query looks like
select <somecolumns>
from users
where <somefilters>;
(you need to use your actual columns and criteria, but Users_SearchUsers is not specified in the question at all). I have ignored paging here for the sake of simplicity
The second query looks like this:
select *
from user_accesses
where access_type_id = 4;
Let's join the two:
select <someoutercolumns>
from
(
select <someinnercolumns>
from users
where <somefilters>
) t1
join
(
select <someotherinnercolumns>
from user_accesses
where access_type_id = 4
) t2
on t1.user_id = t2.user_id;
These queries are probably not the exact solutions you need, but you want the answers to improve, then improve your question.
The requirement makes sense if the LINQ query is very slow. In that case you will need to refactor it in the following manner:
select <somecolumns>
from users
join user_accesses
on users.user_id = user_accesses.user_id and user_accesses.access_type_id = 4
where <somefilters>;
you can use this code
select *(you can put your columns instead *)
from Users
join UserAccesses
on Users.userid = UserAccesses.userid
where UserAccesses.typeid = 4;
I'm brand new to .net MVC, and while I have some basic experience with writing SQL queries, I'm not sure how to go about what I need to do for .NET.
My initial query looks like this:
var results = (from s in db.Members
join sa in db.FocusArea on s.ID equals sa.MemberID
where sa.Area == SearchString
select new { s.ID, s.Name, s.Overview }).ToList();
This is not functioning correctly. It is seaching in the s.Overview for some reason. And, I need to make this query much more complicated. In short, I have three tables I need to search across. And with this query, it is not working:
var conceptResults = (from s in db.Cohorts
join oa in db.OutcomeArea on s.ID equals oa.CohortID
where ((oa.Area.Contains(SearchString))
|| (oa.OutcomeType.Contains(SearchString)))
select new { s.ID, s.Name, s.Overview }).ToList();
I need to use my SearchString to search for matches in both Area and Description in db.FocusArea.
I also need to use my SearchString to search for matches (contains) in another table db.SpecificFocusAreas for column SFocusArea where again the join is the ID/MemberID.
Is there a way to essentially do a join or join type of statement? I don't want to join all three tables because I am looking for results from either of the two joins, not from all joins.
Really odd issue that I cant work out.
I am trying to join two tables in a linq statement to only retrieve records where the record in table 1 has no related rows in table 2.
I have used Joins before but for some reason I cant get VS to recognise the second table in the linq statement.
EG.
var result =
(from pc in _dataSource.Payments
join bc in _dataSource.BouncedCheques
on pc.PaymentID != bc.PaymentID //This is where the error occurs, VS does not recognise "bc"
where pc.CustomerNumber == getAccountNumber
& pc.IsDeleted == false
orderby pc.PaymentDate descending
select new PaymentAllocation
{
PaymentId = pc.PaymentID,
PaymentDate = pc.PaymentDate,
CustomerNumber = pc.CustomerNumber,
ChequeReference = pc.ChequeReference,
PaymentValue = pc.PaymentValue,
AllocatedValue = pc.AllocatedValue,
UnallocatedValue = pc.PaymentValue - pc.AllocatedValue,
ReceivedBy = pc.ReceivedBy,
PaymentType = pc.PaymentType,
PostedDate = pc.PostedDate
});
Basically the problem is that the variable "bc" does not seem to be recognised, however I have several other similar Linq queries that all work well
Any ideas?
Your problem is that the syntax for join uses the keyword equals and not standard boolean operators.
Try replacing your join by a cartesian product of your tables:
from pc in _dataSource.Payments
from bc in _dataSource.BouncedCheques
where
pc.PaymentID != bc.PaymentID
&& pc.CustomerNumber == getAccountNumber
& pc.IsDeleted == false
In the join clause you should use the equals keyword:
try:
on pc.PaymentID equals bc.PaymentID
I have two Tables - tblExpenses and tblCategories as follows
tblExpenses
ID (PK),
Place,
DateSpent,
CategoryID (FK)
tblCategory
ID (PK),
Name
I tried various LINQ approaches to get all distinct records from the above two tables but not with much success. I tried using UNION and DISTINCT but it didnt work.
The above two tables are defined in my Model section of my project which in turn will create tables in SQLite. I need to retrieve all the distinct records from both the tables to display values in gridview.
Kindly provide me some inputs to accomplish this task. I did some research to find answer to this question but nothing seemed close to what I wanted. Excuse me if I duplicated this question.
Here is the UNION, DISTINCT approaches I tried:
DISTINCT # ==> Gives me Repetitive values
(from exp in db.Table<tblExpenses >()
from cat in db.Table<tblCategory>()
select new { exp.Id, exp.CategoryId, exp.DateSpent, exp.Expense, exp.Place, cat.Name }).Distinct();
UNION # ==> Got an error while using UNION
I think union already does the distict when you join the two tables you can try somethin like
var query=(from c in db.tblExpenses select c).Concat(from c in
db.tblCategory select c).Distinct().ToList();
You will always get DISTINCT records, since you are selecting the tblExpenses.ID too. (Unless there are multiple categories with the same ID. But that of course would be really, really bad design.)
Remember, when making a JOIN in LINQ, both field names and data types should be the same. Is the field tblExpenses.CategoryID a nullable field?
If so, try this JOIN:
db.Table<tblExpenses>()
.Join(db.Table<tblCategory>(),
exp => new { exp.CategoryId },
cat => new { CategoryId = (int?)cat.ID },
(exp, cat) => new {
exp.Id,
exp.CategoryId,
exp.DateSpent,
exp.Expense,
exp.Place,
cat.Name
})
.Select(j => new {
j.Id,
j.CategoryId,
j.DateSpent,
j.Expense,
j.Place,
j.Name
});
You can try this queries:
A SELECT DISTINCT query like this:
SELECT DISTINCT Name FROM tblCategory INNER JOIN tblExpenses ON tblCategory.categoryID = tblExpenses.categoryID;
limits the results to unique values in the output field. The query results are not updateable.
or
A SELECT DISTINCTROW query like this:
SELECT DISTINCTROW Name FROM tblCategory INNER JOIN tblExpenses ON tblCategory.categoryID = tblExpenses.categoryID;<br/><br/>
looks at the entire underlying tables, not just the output fields, to find unique rows.
reference:http://www.fmsinc.com/microsoftaccess/query/distinct_vs_distinctrow/unique_values_records.asp