How can I map this SQL using NHibernate Criteria API?
Sql:
SELECT COUNT(*) FROM (
SELECT FirstName, LastName FROM Employees GROUP BY FirstName, LastName
) AS Query
This is a very very simple query, my query has a SubSelect much more complex.
So, any idea?
I found a solution for the question, it's a very big hack but it works as expected.
I had to get the generated SQL and surround it with the SELECT COUNT(*) query. Here is the code to do that:
public ISQLQuery BuildCountQuery(ICriteria criteria)
{
CriteriaImpl c = (CriteriaImpl)criteria;
SessionImpl s = (SessionImpl)c.Session;
string entityOrClassName = ExtractRealClassName(c);
SessionFactoryImpl factory = (SessionFactoryImpl)s.SessionFactory;
String[] implementors = factory.GetImplementors(entityOrClassName);
string implementor = implementors.Length == 0 ? null : implementors[0];
var persister = (IOuterJoinLoadable)factory.GetEntityPersister(implementor);
CriteriaLoader loader = new CriteriaLoader(persister, factory, c, implementor, s.EnabledFilters);
SqlString sql = loader.SqlString.Insert(0, "SELECT COUNT(*) FROM (");
sql = sql.Append(") AS Query");
var parameters = loader.Translator.CollectedParameters;
var sqlQuery = this.session.CreateSQLQuery(sql.ToString());
for (int i = 0; i < parameters.Count; i++)
sqlQuery.SetParameter(i, parameters.ElementAt(i).Value, parameters.ElementAt(i).Type);
return sqlQuery;
}
private string ExtractRealClassName(CriteriaImpl criteria)
{
Type rootEntityType = criteria.GetRootEntityTypeIfAvailable();
if (rootEntityType.GetInterfaces().Contains(typeof(INHibernateProxy)))
return criteria.GetRootEntityTypeIfAvailable().BaseType.FullName;
else
return criteria.EntityOrClassName;
}
DetachedCriteria criteriaEmployees = DetachedCriteria.For<Employees>();
criteriaEmployees.SetProjection(Projections.CountDistinct("FirstName"));
ICriteria executableCriteria = criteriaEmployees.GetExecutableCriteria(Session);
int count = executableCriteria.UniqueResult<int>();
DetachedCriteria can be used to create subqueries. Some examples are in the documentation.
Related
How do I run a raw query in ASP.NET core to return the row count from a table?
Currently, I am doing this and the returned result is -1. I think the return result is based on the number of records affected.
int numberOfRows = await
appDbContext.Database.ExecuteSqlInterpolatedAsync(
$"SELECT CODE FROM [samaster] WHERE CODE={productBrandCode} AND WAREHOUSE={warehouse} ");
Any idea on how to get the count back to numberOfRows variable will be appreciated.
NOTE: The above table is not a model so I need to run a raw query.
Thanks
It is currently not possible to get the query result when using ExecuteSqlInterpolatedAsync. The same applies to any additional LINQ Statements.
You can, however, use the underlying ADO.net Provider:
public IList<IDictionary<string, dynamic>> SelectDynamic(string table)
{
using (var command = Database.GetDbConnection().CreateCommand())
{
command.CommandText = $"SELECT * FROM [{table}]";
command.CommandType = CommandType.Text;
Database.OpenConnection();
using (var result = command.ExecuteReader())
{
var entities = new List<IDictionary<string, dynamic>>();
while (result.Read())
{
var dict = new Dictionary<string, dynamic>();
for (int i = 0; i < result.FieldCount; i++)
{
dict.Add(result.GetName(i), result.GetValue(i));
}
entities.Add(dict);
}
return entities;
}
}
}
Add this to your DbContext Class and Call it with:
using (var context = new MyDbContext()) // Or get it with DI, depends on your application
{
var count = context.SelectDynamic("samaster").Where(d => d["CODE"] == productBrandCode && d["WAREHOUSE"] == warehouse).Count();
}
Beware, however, that this is an expensive operation if you have a lot of rows in your table!
An alternative approach to only fetch the relevant results would be to replace
command.CommandText = $"SELECT * FROM [{table}]";
with
command.CommandText = $"SELECT CODE FROM [samaster] WHERE CODE={productBrandCode} AND WAREHOUSE={warehouse}";
and pass the parameters as function parameters.
public IList<IDictionary<string, dynamic>> SelectDynamic(string productBrandCode, string warehouse)
{...
Also make sure to escape all parameters if they are in any way submitted by user input to prevent SQL Injection Attacks!
There are two common approaches :
A.
int numberOfRows = await appDbContext.Database.ExecuteSqlInterpolatedAsync($"SELECT CODE FROM [samaster] WHERE CODE={productBrandCode} AND WAREHOUSE={warehouse} ").Count();
B.
int numberOfRows = await appDbContext.Database.ExecuteSqlInterpolatedAsync($"SELECT count(*) FROM [samaster] WHERE CODE={productBrandCode} AND WAREHOUSE={warehouse} ").First();
Since nobody gave me the correct answer. I end up using the following.
public async Task<bool> IsAValidProduct(string productBrandCode)
{
int count = 0;
await using DbCommand command = appDbContext.Database.GetDbConnection().CreateCommand();
command.CommandText =
"SELECT COUNT(CODE) FROM [samaster] WHERE CODE=#productBrandCode AND WAREHOUSE=#warehouse ";
command.CommandType = CommandType.Text;
command.Parameters.Add(new SqlParameter("#productBrandCode", SqlDbType.VarChar)
{Value = productBrandCode});
command.Parameters.Add(new SqlParameter("#warehouse", SqlDbType.VarChar)
{Value = warehouse});
await appDbContext.Database.OpenConnectionAsync();
count = (int) await command.ExecuteScalarAsync();
await appDbContext.Database.CloseConnectionAsync();
return count == 1;
}
int c= dbObj.Database.ExecuteSqlRaw(sql); //User this code
Can someone help me convert this SQL Query to EntityFramework LINQ?
DECLARE #UserId varchar(50) = '123'
SELECT
TL.TrackId,
COUNT(*) AS LikeCount,
(SELECT IIF(COUNT(*) > 0, 'true','false') FROM UserTrackLikes WHERE
UserId = #UserId AND TrackId = TL.TrackId) AS IsLiked
FROM TrackList AS TL
LEFT OUTER JOIN UserTrackLikes AS UTL
ON UTL.TrackId = TL.TrackId
GROUP BY TL.TrackId
You can use the query syntax:
int userId = 123;
var result = (from trackList in context.TrackLists
select new
{
trackList.TrackId,
LikeCount = trackList.Likes.Count(),
IsLiked = trackList.Likes.Any(x => x.UserId == userId)
}).ToList();
Assuming that here, Likes is a collection of UserTrackLike, declared like this:
public ICollection<UserTrackLike> Likes { get; set; }
i would like to translate this request in LINQ to SQL:
SELECT * from Agir where NouvelIncident='1' AND facturable is null
My try:
public static List<Agir> GetINDEFAgir()
{
DataClassesActilogDataContext db = ContextSingleton.GetDataContext();
List<Agir> list;
var v = from i in db.Agir
where i.facturable is null && i.NouvelIncident == true
select i;
list = v.ToList();
return list;
}
Looks like "is null" is not allowed in LINQ to SQL... i have a mistake.
Thanks in advance for your help
Use ==, 'is' is to check types
public static List<Agir> GetINDEFAgir()
{
DataClassesActilogDataContext db = ContextSingleton.GetDataContext();
List<Agir> list;
var v = from i in db.Agir
where i.facturable == null && i.NouvelIncident == true
select i;
list = v.ToList();
return list;
}
Doesn't this work?
var v = from i in db.Agir
where i.facturable == null && i.NouvelIncident == true
select i;
Linq-to-SQL should translate that to the proper SQL.
I'm trying to implement paging within my project.
When using NHibernate's IQueryOver syntax as shown below things are working as expected.
public PagedResult<T> ExecutePagedQuery(IQueryOver<T,T> query)
{
SetPaging(query);
var results = query.Future<T>();
var count = query.ToRowCountQuery().FutureValue<int>();
return new PagedResult<T>()
{
TotalItemCount = count.Value,
PageOfResults = results.ToList()
};
}
protected virtual void SetPaging(IQueryOver<T, T> query)
{
var maxResults = PageSize;
var numberToSkip = (PageNumber - 1) * PageSize;
query.Skip(numberToSkip).Take(maxResults);
}
For some queries we are using HQL instead of the IQueryOver syntax however.
I'm wondering if there is an equivalent to "query.ToRowCountQuery().FutureValue< int >()" that can be used when querying when passing an IQuery insead of an IQueryOver to provide the row count.
public PagedResult<T> ExecutePagedQuery(IQuery query)
{
SetPaging(query);
var results = query.Future<T>();
var count = // ToRowCountQueryEquivalent?
return new PagedResult<T>()
{
TotalItemCount = count,
PageOfResults = results.ToList()
};
}
protected virtual void SetPaging(IQuery query)
{
var maxResults = PageSize;
var numberToSkip = (PageNumber - 1) * PageSize;
query.SetFirstResult(numberToSkip);
query.SetMaxResults(maxResults);
}
some crazy idea
string countQuery;
if (query.QueryString.StartsWith("SELECT", StringComparison.OrdinalIgnoreCase))
countQuery = Regex.Replace(query.QueryString, "SELECT (.*) FROM", #"SELECT Count($1) FROM", RegexOptions.IgnoreCase);
else
countQuery = "SELECT COUNT(*) " + query.QueryString;
We've since converted our HQL queries to IQueryOver allowing us to take advantage of the ToRowCountQuery() helper.
Is there a way in NHibernate to check if an object exists in the database without having to get/load the object?
You could use one of the following 3 queries (or you could use Criteria API Projections.RowCountInt64() from David answer):
bool exist = session.Query<Employee>()
.Any(x => x.EmployeeID == 1);
bool exist = session.QueryOver<Employee>()
.Where(x => x.EmployeeID == 1)
.RowCount() > 0;
bool exist = session.Query<Employee>()
.Count(x => x.EmployeeID == 1) > 0;
Just keep in mind that Any is worst of those three because it fetches entity. Here is sql query generated for each:
exec sp_executesql N'select TOP (1) employee0_.EmployeeID as EmployeeID0_, employee0_.Name as Name0_ from Employee employee0_ where employee0_.EmployeeID=#p0',N'#p0 int',#p0=1
exec sp_executesql N'SELECT count(*) as y0_ FROM Employee this_ WHERE this_.EmployeeID = #p0',N'#p0 int',#p0=1
exec sp_executesql N'select cast(count(*) as INT) as col_0_0_ from Employee employee0_ where employee0_.EmployeeID=#p0',N'#p0 int',#p0=1
So I let myself to do some tests with your examples #Jamie Ide #Darius Kucinskas #Dmitry
So:
var exists = session
.CreateQuery("select 1 from Widget where _color = 'green'")
.SetMaxResults(1)
.UniqueResult<Int32?>()
.HasValue;
in my case was 18% faster than
bool exist = session.Query<Employee>()
.Any(x => x.EmployeeID == 1);
14% than
bool exist = session.Query<Employee>()
.Count(x => x.EmployeeID == 1) > 0;
and 8%
bool exist = session.QueryOver<Employee>()
.Where(x => x.EmployeeID == 1)
.RowCount() > 0;
So in my opinion even if hard coded query is fastest the
bool exist = session.QueryOver<Employee>()
.Where(x => x.EmployeeID == 1)
.RowCount() > 0;
is best option because of good habits and code clearness
Could always do a count.
I tend to use DetachedCriteria, so I'd have something like:
var criteria = // some criteria that will identify your object
var result = criteria
.GetExecutableCriteria(Session)
.SetProjection(Projections.RowCountInt64())
.UniqueResult();
return result > 0;
To expand on Darius Kucinskas' excellent answer, you can avoid fetching the entity using Select:
bool exist = session.Query<Employee>()
.Where(x => x.EmployeeID == 1)
.Select(x => x.EmployeeID)
.Any();
As mentioned, the query performance should be the same however I would expect this to reduce network traffic.
I think you are looking for this...
var fooExists = session.Query<Foo>().Any(f => /*condition*/);
var exists = 1 == session.CreateQuery("select 1 from MyEntity where Property = :value")
.SetValue("value", xxx)
.UniqueResult<Int32?>();
Based on Ricardo answer, this seems like the most efficient way to check if object exists using HQL. It doesn't COUNT and doesn't load the object unnecessarily:
var exists = session
.CreateQuery("select 1 from Widget where _color = 'green'")
.SetMaxResults(1)
.UniqueResult<Int32?>()
.HasValue;
It generates this SQL (note that this is SQLite, so LIMIT instead of TOP)
select
1 as col_0_0_
from
Widgets
where
Color='green' limit 1;
You can have a try:
public virtual T FindById<T>(int id)
{
return session.Get(typeof(T), id));
}
I created an extension method from the answers above. I choose to use the Any version but with a Select on the primary key the same amount of data will be returned depend on the primary key type.
public static bool Exists<TModel, TKey>(
this IQueryable<TModel> query, Expression<Func<TModel, TKey>> selector, TKey id)
where TKey : class
{
return query
.Select(selector)
.Any(x => x == id);
}
public static Task<bool> ExistsAsync<TModel, TKey>(
this IQueryable<TModel> query, Expression<Func<TModel, TKey>> selector, TKey id)
where TKey : class
{
return query
.Select(selector)
.AnyAsync(x => x == id);
}