I have the concept of a document that has keyword/s. EF abstracted out the document-keyword joining table to an association.
The structure looks like this
Document: ID (PK)
Document_Keyword: DocumentID (PK), Keyword (PK)
Keyword: Keyword (PK)
I have the requirement to return a list of documents where they contain ALL keywords in a string[]
If I was doing this in SQL it would be similar to below
with t as (
select 'keyword1' KEYWORD union
select 'keyword2'
)
select DocumentID,count(*) from [dbo].[Document_Keyword] p
inner join t on p.KEYWORD = t.KEYWORD
group by DocumentID
having count(*) = (select count(*) from t)
Im struggling to form a linq query that will give me the same result.
I have tried the following LINQ statement however it does returns documents that contain 1 or more of the keywords in the array. I require that documents are only returned if ALL keywords match.
var query = (from k in db.KEYWORD
from b in k.DOCUMENT
join q in arrKeywords //array of string[]
on k.KEYWORD equals q
select new Document()
{
Filename = b.FILENAME,
Description = b.TITLE
});
Any ideas?
Cheers
Jeremy
If I get you well you want entries of which all keywords match exactly, i.e. it doesn't have any other keywords. A way too achieve this is
var kwc = arrKeywords.Count();
var query = from k in db.KEYWORD
let kw = k.DOCUMENT.Select(d => d.KEYWORD)
where kw.All(kw1 => arrKeywords.Contains(kw1))
&& kw.Count() == kwc;
The generated query is still much longer than a hand-coded one would be, but I think the database's query optimizer should be able to handle this.
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,
};
In LINQ, I am trying to inner join custom function written for full-text search and an Iqueryable result.
However, I get the following error when I try to to_ret.select(--something--).ToList()
Nested query does not have appropriate key
LINQ Code:
var sql_query = db.search(st);
var to_ret = from ts in sql_query
from t in table
where t.Id == ts.Value select t;
to_ret = to_ret.Include(x => x.table1)
.Include(x=> x.table2.Select(y=> y.table2Col));
to_ret.select(-something-).toList();
SQL Code:
create function [dbo].[search]
(#keywords nvarchar(4000))
returns table
as
return (
select [key] from containstable(tb,(Name,Description),#keywords)
)
Code that works in place of above LINQ Code :
var ids = (from t in table join ts in db.search(st) on t.Id equals ts.Value select t.Id).ToList();
to_ret = to_ret.Where(x => ids.Contains(x.Id));
However, the code that works isn't efficient enough as it eagerly loads all the ids for comparison
Do not join the table using LINQ, it is not effective.
You need to include all the joined functions into [dbo].[search] table valued function (like a view). Then do just call the [dbo].[search] from EF and filter it.
I have mentioned joined Fulltext table valued function here.
Note that fulltext and filtering together in one query could take time, because it is not easy job for query optimizer. Query optimizer selects to perform first fulltext on entire table(s) and then filtering or the opposite way.
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
I have five tables all with a primary key of ID
User
User_Role_Relation with Foreign Keys User_ID and Role_ID
Role
Role_Right_Relation with Foreign Keys Role_ID and Right_ID
Right
I am currently getting the Rights for the selected User with the following query in a stored procedure
SELECT DISTINCT
tbl_Right.ID, tbl_Right.Name
FROM
tbl_User_Role_Relation
INNER JOIN
tbl_Role_Right_Relation ON tbl_User_Role_Relation.Role_ID = tbl_Role_Right_Relation.Role_ID
INNER JOIN
tbl_Right ON tbl_Role_Right_Relation.Right_ID = tbl_Right.ID
WHERE
tbl_User_Role_Relation.User_ID = #User_ID
I am trying to covert this to LINQ to Entity with this code
var query = from r in context.Rights
from rrr in r.Role_Right_Relation
from rl in rrr.Role
from urr in rl.User_Role_Relation
where urr.User_ID == userid
select r;
but I get the following error
An expression of type 'Models.Role' is not allowed in a subsequent from clause in a query expression with source type 'System.Linq.IQueryable' Type inference failed in the call to 'SelectMany'
Any advise would be helpful.
Thanks.
First of all that linq query is doing a cross join, not inner join like your sql. You should check out this
Second of all, you would probably be best correctly defining the relationships between entities in the edmx and you probably won't have to join at all, instead you can use navigation properites to access parent/children and filter on those properties directly
The idea of the entity framework is you don't have to flatten the hierarchy
Edit 3
If you posted your code verbatim, then you are missing a line
from u in urr.Users
So:
var query = from r in context.Rights
from rrr in r.Role_Right_Relation
from rl in rrr.Role
from urr in rl.User_Role_Relation
from u in urr.Users
where u.User_ID == userid
select r;
Or at least there's a typo and the where should read:
where urr.User_ID == userid
resulting in:
var query = from r in context.Rights
from rrr in r.Role_Right_Relation
from rl in rrr.Role
from urr in rl.User_Role_Relation
where urr.User_ID == userid
select r;
If you use method syntax you should be able to do something like:
var user = context.Users.FirstOrDefault(u => u.Id == userId);
var rights =user.Roles.SelectMany(role => role.Rights).Distinct();
Be sure to check user is not null before getting rights
I have a Category table with a tree structure (Id,MasterId)
I'd like to select all products that belong to a Category and all Child Categories.
Today I use this SQL Query which works, but I'd like to add pagination and that would be easier with a pure LINQ query. I use Entity Framework 4.
#Count int = 100,
#CategoryId int
with mq as
(
select c.Id as parent, c.Id as child
from dbo.Categories c
where c.Id = #CategoryId
union all
select q.child, c.Id
from mq q
inner join dbo.Categories c on q.child = c.MasterId
)
select top (#Count) P.* from Products P
inner join ProductToCategory PC ON(PC.ProductId = P.Id)
where PC.CategoryId in (
select child from mq
)
and P.PublishStatus = 1
order by P.PublishedDate DESC;
Any ideas how to get a nice LINQ query on this with pagination (current page, number of products per page, total product count)?
This is recursive / hiearchical query with table expression. EF does not provide support for such queries. If you want to receive data by single roundtrip to DB you must wrap it in stored procedure and import that procedure to your entity framework model.
Paging in SQL is also possible when using table expressions and ROW_NUMBER().
there is an idea. i haven't tested it, so dont blame if it doesn't work :P
var ids = context.TreeItems.Where(x => x.Id == parentId).Select(x => (int?)x.Id);
var tmp = ids;
while (true)
{
IQueryable<int?> localIds = tmp;
var subIds = context.TreeItems.Where(x => ids.Contains(x.ParentId)).Select(x => (int?)x.Id);
if (subIds.Any())
{
tmp = subIds;
ids = ids.Union(subIds);
}
else
break;
}
var allSubItems = context.TreeItems.Where(x => ids.Contains(x.Id));