I did my best search to convert PARTION BY command from TSQL to LINQ command. But apparently there is no way to convert it.
This is my code to which I am going to convert:
WITH MyRowSet
AS
(
SELECT OrderDate
,SalesOrderNumber
,AccountNumber
,CustomerID
,ROW_NUMBER() OVER (PARTITION BY CustomerID ORDER BY CustomerID, OrderDate DESC) AS RowNum
FROM [Sales].[SalesOrderHeader]
)
SELECT * FROM MyRowSet WHERE RowNum = 1
If exist any solution I would be greatful to know.
linq2db has this feature among with CTE. If you already work with EF Core, you can extend your LINQ queries by extension linq2db.EntityFrameworkCore
This SQL can be written by LINQ
var rnQuery =
from oh in db.SalesOrderHeader
select new
{
oh.OrderDate,
oh.SalesOrderNumber,
oh.AccountNumber,
oh.CustomerID,
RowNum = Sql.Ext.RowNumber().Over().PartitionBy(oh.CustomerID)
.OrderByDesc(oh.OrderDate).ToValue()
};
// switch to alternative LINQ Translator
rnQuery = rnQuery.ToLinqToDB();
var query =
from q in rnQuery.AsCte("MyRowSet")
where q.RowNum == 1
select q;
I have simplified your OrderBy - CustomerID is not needed if you are making partition by this field.
Related
I'm trying implement the follow query in LINQ, but I don't find solution:
SQL:
SELECT COUNT(*) AS AmountMonths
FROM (SELECT SUBSTRING(CONVERT(NVARCHAR(12), pay_date, 112), 1, 6) AS Month
FROM #tmp
GROUP BY SUBSTRING(CONVERT(NVARCHAR(12), pay_date, 112), 1, 6)) AS AmountMonths
What I need is get the amounts of months in which the clients made payments, with the condition that there may be months in which no payments have been made.
In C# I tried the following:
int amountMonths = payDetail.GroupBy(x => Convert.ToDateTime(x.PayDate)).Count();
and
int amountMonths = payDetail.GroupBy(x => Convert.ToDateTime(x.PayDate).Month).Count();
But I am not getting the expected result.
(Assuming you're using EF Core)
You're almost there. You could do:
var amountMonths = context.AmountMonths.GroupBy(c => new { c.PayDate.Year, c.PayDate.Month }).Count();
This will translate to something like:
SELECT COUNT(*)
FROM (
SELECT DATEPART(year, [a].[PayDate]) AS [a]
FROM [AmountMonths] AS [a]
GROUP BY DATEPART(year, [a].[PayDate]), DATEPART(month, [a].[Pay_Date])
) AS [t]
which I'd find preferable over creating a string and chopping it up. EOMONTH isn't a standard mapped function, alas, otherwise it can be used to convert a date to month level granularity
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.
I'm using Entity Framework to get the total row count for a table. I simply want the row count, no where clause or anything like that. The following query works, but is slow. It took about 7 seconds to return the count of 4475.
My guess here is that it's iterating through the entire table, just like how IEnumerable.Count() extension method works.
Is there a way I can get the total row count "quickly"? is there a better way?
public int GetLogCount()
{
using (var context = new my_db_entities(connection_string))
{
return context.Logs.Count();
}
}
You can even fire Raw SQL query using entity framework as below:
var sql = "SELECT COUNT(*) FROM dbo.Logs";
var total = context.Database.SqlQuery<int>(sql).Single();
That is the way to get your row count using Entity Framework. You will probably see faster performance on the second+ queries as there is an initialization cost the first time that you run it. (And it should be generating a Select Count() query here, not iterating through each row).
If you are interested in a faster way to get the raw row count in a table, then you might want to try using a mini ORM like Dapper or OrmLite.
You should also make sure that your table is properly defined (at the very least, that it has a Primary Key), as failure to do this can also affect the time to count rows in the table.
If you have access to do so, it would be much quicker to query the sys tables to pull this information.
E.g.
public Int64 GetLogCount()
{
var tableNameParam = new SqlParameter("TableName", "Logs");
var schemaNameParam = new SqlParameter("SchemaName", "dbo");
using (var context = new my_db_entities(connection_string))
{
var query = #"
SELECT ISNULL([RowCount],0)
FROM (
SELECT SchemaName,
TableName,
Sum(I.rowcnt) [RowCount]
FROM sysindexes I
JOIN sysobjects O (nolock) ON I.id = o.id AND o.type = 'U'
JOIN (
SELECT so.object_id,
ss.name as SchemaName,
so.name as TableName
FROM sys.objects SO (nolock)
JOIN sys.schemas SS (nolock) ON ss.schema_id = so.schema_id
) SN
ON SN.object_id = o.id
WHERE I.indid IN ( 0, 1 )
AND TableName = #TableName AND SchemaName = #SchemaName
GROUP BY
SchemaName, TableName
) A
";
return context.ExecuteStoreQuery<Int64>(query, tableNameParam, schemaNameParam).First();
}
}
This might be one of those situations where plain SQL commands are better than LINQ. Here's a simplified version of the SQL statement I'm trying to translate:
SELECT * FROM IDTable AS idt
INNER JOIN NameTable AS nt ON nt.IDTableID=idt.Id
AND nt.Id= (SELECT TOP(1) Id
FROM NameTable AS nt2
WHERE nt2.IDTableID=11 ORDER BY nt2.DateInserted DESC)
I have the LINQ query to pull records when just joining on IDs and I've seen how to join on multiple columns, but I have no idea how to plug the subquery into the mix.
If this isnt entirely clear, please let me know and I'll edit to elaborate.
Maybe something like this?
var results = from id in db.IDTable
join n in db.NameTable on id.Id equals n.IDTableID
where n.Id = (
from n2 in db.NameTable
where n2.IDTableID = 11
orderby n2.DateInserted desc
).First()
select new { id, n };
Hi guys I need to rewrite the sql query below using Linq to entity. Unfortunately I don't have a lot of experience of using Linq. Please help me
With TempTableName AS
(SELECT [ColumnName],
[ColumnName2],
[ColumnName3],
[ColumnName4],
ROW_NUMBER() OVER (order by ColumnName desc) as RowNumber from TableName )
SELECT
[ColumnName],
[ColumnName2],
[ColumnName3],
[ColumnName4]
FROM TempTableName WHERE ROWNUMBER
Between 10 and 100
(from t in dbContext.TableName
order by ColumnName descending
select new { ColumnName = t.ColumnName, ColumnName2 = t.ColumnName2 /* ... */ })
.Skip(9)
.Take(91)
If you want to work all the columns from TableName, you can also use select t, this. Probably easier to use, but this will fetch all columns, and it is not clear from your question if that is what you want.