Just assume a simple example:I have two table and use this query:
select *
from People
where PersonGuid = (select PersonGuid from Sellers where Guid = '')
How can I write this query with linq?
I tried this:
var person = from p in loginContext.Person where p.PersonGuid =
(loginContext.Seller.Where(s => s.Guid == sellerGuid).FirstOrDefaultAsync());
but that's wrong.
What is the right way to write it?
If you were to rewrite your SQL query as
select *
from People AS PE
JOIN
Sellers AS Sellers
ON PE.PersonGuid = SE.PersonGuid
WHERE
SE.Guid = ''
then the LINQ becomes a little more obvious:
var person = (from p in loginContext.Person
join s in loginContext.Seller on p.PersonGuid equals s.PersonGuid
where s.guid == ""
select p)
.FirstOrDefault();
Although your SQL would suggest FirstOrDefault is not required.
Warning - not tested.
You could probably try using LINQ JOIN clause.
It should be something like:
from p in loginContext.Person
join s in loginContext.Seller on new { p.PersonGuid = s.Guid }
where s.Guid = sellerGuid
You can know more about LINQ JOIN here -> Microsoft C# Reference
Hope it helps!
I will assume that select PersonGuid from Sellers where Guid = '' will provide a single value no matter what, otherwise your SQL statement would fail.
Accepted answer works, but if you want a solution that keeps the spirit of the SQL query, you can rely on Any function. Something along the following:
var person = await loginContext.Person
.Where(p => loginContext.Sellers
.Any(s => s.PersonGuid == p.PersonGuid && s.Guid = ""))
.FirstOrDefaultAsync();
I expect this to be transformed into an SELECT ... WHERE EXISTS which is similar to your initial query.
Related
The query when not trying any SQL injection fix works perfectly there is no any connection issue. It is only when trying to change the query to protect it from injections, when the syntax breaks.
I am trying to secure this raw query preventing sql injection
I have seen in the docs (and I know the prepared statements from goo'ol php)
and that Laravel shows a simple example such as this one:
$results = DB::select('select * from users where id = :id', ['id' => 1]);
or this one
$users = DB::select('select * from users where active = ?', [1]);
I am trying to do that where it corresponds, at the WHERE clause equaling the variable provided from the form $a, but all attempts break the syntax.
so anything like:
where author = ?, [$ba], or '$ba' or where author = :ba, ['author' => '$ba']
gives syntax errors.
$ba = 'whatever';
$results =
DB::select(DB::raw("SELECT
t.id, t.AvgStyle, r.RateDesc
FROM (
SELECT
p.id, ROUND(AVG(s.Value)) AS AvgStyle
FROM posts p
INNER JOIN styles s
ON s.post_id = p.id
WHERE author = '$ba'
GROUP BY p.id
) t
INNER JOIN rates r
ON r.digit = t.AvgStyle"
));
Thank you.
Note> question is not eligible for bounties. It is someone always putting it on every question of mine without my permission.
The answer was extremely close to what Everton said: It just needed to go one parentheses to the right.
That is:
, )[$ba]);
You can try this way:
$ba = 'whatever';
$results =
DB::select(DB::raw("SELECT
t.id, t.AvgStyle, r.RateDesc
FROM (
SELECT
p.id, ROUND(AVG(s.Value)) AS AvgStyle
FROM posts p
INNER JOIN styles s
ON s.post_id = p.id
WHERE author = ?
GROUP BY p.id
) t
INNER JOIN rates r
ON r.digit = t.AvgStyle"
, )[$ba]); // #everton We just needed to move it one parentheses
The important thing here is that you need to respect the order if you have others parameters.
I need nhiberante query (not HQL) equivalent following SQL:
SELECT ur.*
FROM (SELECT MAX(requestTime) rt, macAddress ma
FROM UpdateRequests
GROUP BY macAddress) mur
JOIN dbo.UpdateRequests ur
ON mur.ma = ur.macAddress AND mur.rt = ur.requestTime
I had no luck with other similar examples on stackoverflow.
Having UpdateRequest mapping, it seems that is not possible with Query API, how about QueryOver?
Finally one Guru suggested me to change SQL query without changing execution plan:
SELECT ur.*
FROM [dbo].[UpdateRequests] AS ur
WHERE ur.[RequestTime] = (SELECT MAX(mur.[RequestTime])
FROM [dbo].[UpdateRequests] mur
WHERE mur.[MacAddress] = ur.[MacAddress])
So in code it transforms into:
session
.Query<UpdateRequest>()
.Where(ur => ur.RequestTime == session.Query<UpdateRequest>()
.Where(mur => mur.MacAddress == ur.MacAddress)
.Max(mur => mur.RequestTime))
.ToList();
And this is exactly what i need.
When this gets called two times, the second invocation doesn't re-run the query on the database, the query caching works.
var query = from p in session.Query<Product>()
where p.YearIntroduced >= 0
select p;
query = query.Cacheable();
var t = query.ToList();
However, when I put some join on the query, the query cache is not working anymore, hence when this is invoked two times, the query is invoked on database two times too:
var query = from p in session.Query<Product>()
join l in session.Query<ProductLanguage>()
on p.ProductId equals l.ProductId
where p.YearIntroduced >= 0
select new { p, l };
query = query.Cacheable();
var t = query.ToList();
Might be a dumb question, is query caching can work on one table only, hence when adding a join, the query is not cacheable anymore?
What's the solution to make a query cacheable even it has a join?
Another oddity, the query caching with join will work if I remove the where clause. When this gets called two times, the second invocation doesn't re-run the query on database, the query caching works
var query = from p in session.Query<Product>()
join l in session.Query<ProductLanguage>()
on p.ProductId equals l.ProductId
select new { p, l };
query = query.Cacheable();
var t = query.ToList();
But what's the use of a query when you can't put a where clause on it?
Is this an NHibernate bug, or am I just using query caching the wrong way?
Found the solution, put the Where clause on the final part of the query:
var query = from p in session.Query<Product>()
join l in session.Query<ProductLanguage>()
on p.ProductId equals l.ProductId
select new { p, l };
query = query.Where(x => x.p.ProductId && x.l.LanguageCode == "en").Cacheable();
var t = query.ToList();
I have write the below query in simple SQL,
I want to change it to use LINQ, I have tried, but my LINQ query and the original SQL statement are giving different record sets.
Simple SQL Query:
select *
from Paymentadvices
where status = 3
and Id in (select PaymentAdviceId from Approvals where ApprovedById = 13)
LINQ:
var myPaymentAdviceList = from pa in db.PaymentAdvices
where pa.Status == 3
join Ap in db.Approvals on pa.Id equals
Ap.PaymentAdviceId
where Ap.EmployeeId == 13
orderby pa.PaidDate descending
select pa;
I am not supposed to use join I guess, What should I use ?
var a = db.Approvals.Where( x => x.ApprovalById = 13).PaymentAdviceId;
var b = db.Paymentadvices.Where(x => x.status ==3 && a.Contains(x.Id);
.Contains() makes the WHERE IN () , you don't need a join there
var a = from a in db.Approvals
where a.ApprovedById == 3
select a.PaymentAdviceId;
var b = (from p in db.PaymentAdvices
where p.Status == 3 &&
a.Contains(p.Id)
select p).ToList();
those are both linq , the top is just lambda expressions which are commonly used in Linq queries. I would reccommend that you get used to reading/ writing both styles . The majority of code you'll come across in lambda style
I believe something like the below would work:
var query = from p in db.PaymentAdvices
where p.Status == 3 && db.Approvals
.Select(a => a.Id)
.Where(a => a.ApprovedById == 13)
.Contains(p.Id)
select p;
Though it's worth noting that #Scott Selby and #axrwkr solutions above are essentially the exact same thing in another form.
I'm trying to convert "SQL Outer Apply" to Linq.
The SQL is:
select Currencies.Name, Currencies.Sign ,a.ActualPrice
from Currencies
outer apply (select CurrencyID,ActualPrice from Prices
where ProductID=5 and Currencies.ID=Prices.CurrencyID)a
I have tried the following Linq but got one row, instead of row for each currency as the SQL statement gives me.
from c in Currencies
from p in Prices.DefaultIfEmpty()
where p.ProductID.Equals(5) && c.ID==p.CurrencyID
select new {c.Name, p.ActualPrice}
Any solution for this?
Try this:
var result =
Currencies.Select(c => new
{
Name = c.Name,
Sign = c.Sign,
ActualPrice = Prices.Where(p => p.ProductID == 5 &&
p.CurrencyID == c.ID)
.FirstOrDefault()
});
I am not sure if this returns the correct result, because I don't know what happens, when the subselect in outer apply returns multiple rows...