I’m having a problem with translating T-SQL query into Nhibernate query – or writing query that will return same results but will be properly written in NH query language (HQL, Criteria, QueryOver, LINQ – I don’t truly care).
I would like to execute similar query from NHibernate:
SELECT
lic.RegNo,
lic.ReviewStatus
FROM
Licence lic
WHERE
lic.RegNo IN
(
SELECT
grouped.RegNo
FROM
(
SELECT
g.[Type],
g.Number,
MAX(g.Iteration) AS [Iteration],
MAX(g.RegNo) AS [RegNo]
FROM
Licence g
GROUP BY
g.[Type],
g.Number
) as grouped
)
ORDER BY
lic.RegNo desc
It returns the top most licenses and fetch their review status if exists. RegNo is created from Type, Number and Iteration (pattern: {0}{1:0000}-{2:00}). Each license can have multiply iterations and some of them can contains ReviewStatus, for instance:
W0004-01 NULL
W0001-03 1
P0004-02 3
P0001-02 4
If iteration part is greater than 1 it means that there are multiply iterations (n) for specific licence.
I’ve manage to create NH query by going twice to database:
LicenceInfoViewModel c = null;
var grouped = session.QueryOver<Licence>()
.SelectList(l => l
.SelectGroup(x => x.Type)
.SelectGroup(x => x.Number)
.SelectMax(x => x.Iteration)
.SelectMax(x => x.RegNo).WithAlias(() => c.RegNo)
).TransformUsing(Transformers.AliasToBean<LicenceInfoViewModel>())
.Future<LicenceInfoViewModel>();
var proper = session.QueryOver<Licence>()
.Select(x => x.RegNo, x => x.ReviewStatus)
.WhereRestrictionOn(x => x.RegNo)
.IsIn(grouped.Select(x => x.RegNo).ToArray())
.TransformUsing(Transformers.AliasToBean<LicenceInfoViewModel>())
.List<LicenceInfoViewModel>();
// ...
public class LicenceInfoViewModel
{
public string RegNo { get; set; }
public LicReviewStatus? ReviewStatus { get; set; }
}
public enum LicReviewStatus
{
InProgress,
Submitted,
Validated,
RequestForInformation,
DecissionIssued
}
However this solution is not good as it require to download all grouped licences from database, and there could be a thousands of them.
Is there a better way to write this query or is there a way to translate provided above T-SQL query into NHibernate?
adding nhibernate and hibernate tags as IMO if this can be done in hibernate it should be easily translated into nh
I don't think that SQL does what you think it does. Iteration is not used for anything.
In any case, it seems unnecessary. You can change the WHERE to the following, and you'll have both valid SQL and HQL:
lic.RegNo IN
(
SELECT
MAX(g.RegNo)
FROM
Licence g
GROUP BY
g.Type,
g.Number
)
Related
Hello i'm trying to get all users which have had payments at least 6 months over the given period (which must be a year). I've written SQL which works fine, but i have difficulties trying to convert it to nhibernate.
SQL:
SELECT COUNT(UserId) AS paidMonthsCount, UserId FROM (
SELECT DISTINCT UserId,
YEAR(PayDate) as _year,
MONTH(PayDate) as _month
FROM Payments
WHERE PayDate >= '2014-04-02T00:00:00' AND PayDate < '2015-04-02T23:59:00'
)result GROUP BY result.UserId
i have converted inner SQL:
var subQuery = Session.QueryOver(() => paymentAlias)
.SelectList(list => list
.Select(Projections.Distinct(Projections.Property<VelferdPayment>(p => p.Client.Id)).WithAlias(() => userWithHelp.Id))
.Select(p => p.AssignmentYear).WithAlias(() => userWithHelp.AssignmentDate)
)
.WhereRestrictionOn(p => p.AssignmentDate)
.IsBetween(parameters.FromDate)
.And(parameters.ToDate);
which selects the distinct part and i have the other part which is selecting from result:
var query = Session.QueryOver(() => userWithHelp).
SelectList(list => list
.SelectCount(p=> p.Id).WithAlias(()=> userWithHelpCount.Count)
.SelectGroup(p => p.Id).WithAlias(() => userWithHelpCount.Id)
)
.TransformUsing(Transformers.AliasToBean<UserWithHelpCount>())
.List<UserWithHelpCount>();
How can i queryover the subQuery results or is it possible to write single request to SQL. Working for a long time please help.
In general, with NHibernate we can only (or mainly) query Entities, not TABLES. Other words, we firstly map tables or views or even some <subselect>s into entities. The below mapping of the User (C# object User)
<class name="user" table="[dbo].[user_table]" ...
Will allow us to create query over C# User.
session.QueryOver<User>()...
Behind the scene it will generate FROM clause, which will contain the content of table attribute, i.e. FROM [dbo].[user_table]
That's it. There is no other way how to set the generated FROM clause. Just by mapping.
But there is a way which allow us to use existing ADO.NET connection to create custom query and even convert its result to some entity, or DTO. It is CreateSQLQuery() API:
17.1.5. Returning non-managed entities
It is possible to apply an IResultTransformer to native sql queries. Allowing it to e.g. return non-managed entities.
sess.CreateSQLQuery("SELECT NAME, BIRTHDATE FROM CATS")
.SetResultTransformer(Transformers.AliasToBean(typeof(CatDTO)))
This query specified:
the SQL query string
a result transformer
The above query will return a list of CatDTO which has been instantiated and injected the values of NAME and BIRTHNAME into its corresponding properties or fields.
So, we can use native SQL SELECT statements to get any results. We can even create some custom DTO and let NHibernate to transform result into them...
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 }));
Domain Model
I've got a canonical Domain of a Customer with many Orders, with each Order having many OrderItems:
Customer
public class Customer
{
public Customer()
{
Orders = new HashSet<Order>();
}
public virtual int Id {get;set;}
public virtual ICollection<Order> Orders {get;set;}
}
Order
public class Order
{
public Order()
{
Items = new HashSet<OrderItem>();
}
public virtual int Id {get;set;}
public virtual Customer Customer {get;set;}
}
OrderItems
public class OrderItem
{
public virtual int Id {get;set;}
public virtual Order Order {get;set;}
}
Problem
Whether mapped with FluentNHibernate or hbm files, I run two separate queries, that are identical in their Fetch() syntax, with the exception of one including the .First() extension method.
Returns expected results:
var customer = this.generator.Session.Query<Customer>()
.Where(c => c.CustomerID == id)
.FetchMany(c => c.Orders)
.ThenFetchMany(o => o.Items).ToList()[0];
Returns only a single item in each collection:
var customer = this.generator.Session.Query<Customer>()
.Where(c => c.CustomerID == id)
.FetchMany(c => c.Orders)
.ThenFetchMany(o => o.Items).First();
I think I understand what's going on here, which is that the .First() method is being applied to each of the preceding statements, rather than just to the initial .Where() clause. This seems incorrect behavior to me, given the fact that First() is returning a Customer.
Edit 2011-06-17
After further research and thinking, I believe that depending on my mapping, there are two outcomes to this Method Chain:
.Where(c => c.CustomerID == id)
.FetchMany(c => c.Orders)
.ThenFetchMany(o => o.Items);
NOTE: I don't think I can get subselect behavior, since I'm not using HQL.
When the mapping is fetch="join" I should get a cartesian product between the Customer, Order and OrderItem tables.
When the mapping is fetch="select" I should get a query for Customer, and then multiple queries each for Orders and OrderItems.
How this plays out with adding the First() method to the chain is where I lose track of what should be happening.
The SQL Query that get's issued is the traditional left-outer-join query, with select top (#p0) in front.
The First() method is translated into SQL (T-SQL at least) as SELECT TOP 1 .... Combined with your join fetching, this will return a single row, containing one customer, one order for that customer and one item for the order. You might consider this a bug in Linq2NHibernate, but as join fetching is rare (and I think you're actually hurting your performance pulling the same Customer and Order field values across the network as part of the row for each Item) I doubt the team will fix it.
What you want is a single Customer, then all Orders for that customer and all Items for all those Orders. That happens by letting NHibernate run SQL that will pull one full Customer record (which will be a row for each Order Line) and construct the Customer object graph. Turning the Enumerable into a List and then getting the first element works, but the following will be slightly faster:
var customer = this.generator.Session.Query<Customer>()
.Where(c => c.CustomerID == id)
.FetchMany(c => c.Orders)
.ThenFetchMany(o => o.Items)
.AsEnumerable().First();
the AsEnumerable() function forces evaluation of the IQueryable created by Query and modified with the other methods, spitting out an in-memory Enumerable, without slurping it into a concrete List (NHibernate can, if it wishes, simply pull enough info out of the DataReader to create one full top-level instance). Now, the First() method is no longer applied to the IQueryable to be translated to SQL, but it is instead applied to an in-memory Enumerable of the object graphs, which after NHibernate has done its thing, and given your Where clause, should be zero or one Customer record with a hydrated Orders collection.
Like I said, I think you're hurting yourself using join fetching. Each row contains the data for the Customer and the data for the Order, joined to each distinct Line. That is a LOT of redundant data, which I think will cost you more than even an N+1 query strategy.
The best way I can think of to handle this is one query per object to retrieve that object's children. It would look like this:
var session = this.generator.Session;
var customer = session.Query<Customer>()
.Where(c => c.CustomerID == id).First();
customer.Orders = session.Query<Order>().Where(o=>o.CustomerID = id).ToList();
foreach(var order in customer.Orders)
order.Items = session.Query<Item>().Where(i=>i.OrderID = order.OrderID).ToList();
This requires a query for each Order, plus two at the Customer level, and will return no duplicate data. This will perform far better than a single query returning a row containing every field of the Customer and Order along with each Item, and also better than sending a query per Item plus a query per Order plus a query for the Customer.
I'd like to update the answer with my found so that could help anybody else with the same problem.
Since you are querying the entity base on their ID, you can use .Single instead of .First or .AsEnumerable().First():
var customer = this.generator.Session.Query<Customer>()
.Where(c => c.CustomerID == id)
.FetchMany(c => c.Orders)
.ThenFetchMany(o => o.Items).Single();
This will generate a normal SQL query with where clause and without the TOP 1.
In other situation, if the result has more than one Customer, exception will be thrown so it won't help if you really need the first item of a series based on condition. You have to use 2 queries, one for the first Customer and let the lazy load do the second one.
Imagine the following (simplified) database layout:
We have many "holiday" records that relate to going to a particular Accommodation on a certain date etc.
I would like to pull from the database the "best" holiday going to each accommodation (i.e. lowest price), given a set of search criteria (e.g. duration, departure airport etc).
There will be multiple records with the same price, so then we need to choose by offer saving (descending), then by departure date ascending.
I can write SQL to do this that looks like this (I'm not saying this is necessarily the most optimal way):
SELECT *
FROM Holiday h1 INNER JOIN (
SELECT h2.HolidayID,
h2.AccommodationID,
ROW_NUMBER() OVER (
PARTITION BY h2.AccommodationID
ORDER BY OfferSaving DESC
) AS RowNum
FROM Holiday h2 INNER JOIN (
SELECT AccommodationID,
MIN(price) as MinPrice
FROM Holiday
WHERE TradeNameID = 58001
/*** Other Criteria Here ***/
GROUP BY AccommodationID
) mp
ON mp.AccommodationID = h2.AccommodationID
AND mp.MinPrice = h2.price
WHERE TradeNameID = 58001
/*** Other Criteria Here ***/
) x on h1.HolidayID = x.HolidayID and x.RowNum = 1
As you can see, this uses a subquery within another subquery.
However, for several reasons my preference would be to achieve this same result in NHibernate.
Ideally, this would be done with QueryOver - the reason being that I build up the search criteria dynamically and this is much easier with QueryOver's fluent interface. (I had started out hoping to use NHibernate Linq, but unfortunately it's not mature enough).
After a lot of effort (being a relative newbie to NHibernate) I was able to re-create the very inner query that fetches all accommodations and their min price.
public IEnumerable<HolidaySearchDataDto> CriteriaFindAccommodationFromPricesForOffers(IEnumerable<IHolidayFilter<PackageHoliday>> filters, int skip, int take, out bool hasMore)
{
IQueryOver<PackageHoliday, PackageHoliday> queryable = NHibernateSession.CurrentFor(NHibernateSession.DefaultFactoryKey).QueryOver<PackageHoliday>();
queryable = queryable.Where(h => h.TradeNameId == website.TradeNameID);
var accommodation = Null<Accommodation>();
var accommodationUnit = Null<AccommodationUnit>();
var dto = Null<HolidaySearchDataDto>();
// Apply search criteria
foreach (var filter in filters)
queryable = filter.ApplyFilter(queryable, accommodationUnit, accommodation);
var query1 = queryable
.JoinQueryOver(h => h.AccommodationUnit, () => accommodationUnit)
.JoinQueryOver(h => h.Accommodation, () => accommodation)
.SelectList(hols => hols
.SelectGroup(() => accommodation.Id).WithAlias(() => dto.AccommodationId)
.SelectMin(h => h.Price).WithAlias(() => dto.Price)
);
var list = query1.OrderByAlias(() => dto.Price).Asc
.Skip(skip).Take(take+1)
.Cacheable().CacheMode(CacheMode.Normal).List<object[]>();
// Cacheing doesn't work this way...
/*.TransformUsing(Transformers.AliasToBean<HolidaySearchDataDto>())
.Cacheable().CacheMode(CacheMode.Normal).List<HolidaySearchDataDto>();*/
hasMore = list.Count() == take;
var dtos = list.Take(take).Select(h => new HolidaySearchDataDto
{
AccommodationId = (string)h[0],
Price = (decimal)h[1],
});
return dtos;
}
So my question is...
Any ideas on how to achieve what I want using QueryOver, or if necessary Criteria API?
I'd prefer not to use HQL but if it is necessary than I'm willing to see how it can be done with that too (it makes it harder (or more messy) to build up the search criteria though).
If this just isn't doable using NHibernate, then I could use a SQL query. In which case, my question is can the SQL be improved/optimised?
I have manage to achieve such dynamic search criterion by using Criteria API's. Problem I ran into was duplicates with inner and outer joins and especially related to sorting and pagination, and I had to resort to using 2 queries, 1st query for restriction and using the result of 1st query as 'in' clause in 2nd creteria.
public class City
{
virtual public long Id { get; set; }
virtual public string Name { get; set; }
}
City table contains duplicated Names and I want to remove duplicates. I also want the results to be ordered by Id.
First I thought about the following query.
select distinct Name from City order by Id;
But this breaks with 'ORDER BY items must appear in the select list if SELECT DISTINCT is specified.' exception. After seeing http://weblogs.sqlteam.com/jeffs/archive/2007/12/13/select-distinct-order-by-error.aspx I think I should do:
select Name from City group by Name order by min(Id)
So my question is how can I do this query with QueryOver?
This is possible in ICriteria:
var list =
session.CreateCriteria<City>()
.SetProjection(Projections.Group("Name"))
.AddOrder(Order.Asc(Projections.Min("Id")))
.List<string>();
But this is not currently possible in QueryOver, because the .OrderBy(IProjection) overload is missing. Once the missing overload has been added it should look something like:
var list =
s.QueryOver<City>()
.Select(Projections.Group<City>(p => p.Name))
.OrderBy(Projections.Min<City>(c => c.Id)).Asc
.List<string>();
Note that the Projections overloads are there just now, so you can write the following (typesafe) query in ICriteria:
var list =
session.CreateCriteria<City>()
.SetProjection(Projections.Group<City>(c => c.Name))
.AddOrder(Order.Asc(Projections.Min<City>(c => c.Id)))
.List<string>();
So, what I've found is pretty simple...
var query = session.QueryOver<MyModel>()
// Conditions here
.OrderBy(m => m.GetThisDistinctField).Desc() // ...or Asc()...
.SelectList(m => m.SelectGroup(g => g.GetThisDistinctField));
var result = query.List<FieldDataType>().ToList();
return result;
To get an ordered query in queryover, start with a query that includes whatever criteria you need, but then add the SelectList/SelectGroup setup in order to get the distinct list. In other words, it's sort of like NHibernate can take a regular query, and then do special stuff to make it a select distinct query.
This is a solution I'm using in a current project I'm working on; I hope it helps someone else too.