How do I do this
SELECT CEILING(COUNT(*) / 10) NumberOfPages
FROM MyTable
in Linq to SQL?
Many .NET methods are translated to SQL Server functions, such as most of the methods of the Math class and the String class. But there are some caveats.
Also have a look at the SqlMethods class, which exposes additional SQL Server function that doesn't have a .NET equivalent.
But you don't even need any of that in your case:
int numberOfPages;
using (var db = new MyDBDataContext())
{
numberOfPages = (int)Math.Ceiling(db.Books.Count() / 10.0);
}
You dont use SQL CEILING, you use .NET ceiling (Math.Ceiling) in your LINQ query.
I don't think this is possible.
A possible solution would be to get the total count and then figure it out in .NET code.
Like below:
where query is IQueryable
var itemsPerPage = 10;
var currentPage = 0;
var totalResults = query.Count();
var myPagedResults = query.Skip(currentPage).Take(itemsPerPage);
var totalPages = (int)Math.Ceiling((double)totalResults / (double)pageSize);
Related
I am currently updating a BackEnd project to .NET Core and having performance issues with my Linq queries.
Main Queries:
var queryTexts = from text in _repositoryContext.Text
where text.KeyName.StartsWith("ApplicationSettings.")
where text.Sprache.Equals("*")
select text;
var queryDescriptions = from text in queryTexts
where text.KeyName.EndsWith("$Descr")
select text;
var queryNames = from text in queryTexts
where !(text.KeyName.EndsWith("$Descr"))
select text;
var queryDefaults = from defaults in _repositoryContext.ApplicationSettingsDefaults
where defaults.Value != "*"
select defaults;
After getting these IQueryables I run a foreach loop in another context to build my DTO model:
foreach (ApplicationSettings appl in _repositoryContext.ApplicationSettings)
{
var applDefaults = queryDefaults.Where(c => c.KeyName.Equals(appl.KeyName)).ToArray();
description = queryDescriptions.Where(d => d.KeyName.Equals("ApplicationSettings." + appl.KeyName + ".$Descr"))
.FirstOrDefault()?
.Text1 ?? "";
var name = queryNames.Where(n => n.KeyName.Equals("ApplicationSettings." + appl.KeyName)).FirstOrDefault()?.Text1 ?? "";
// Do some stuff with data and return DTO Model
}
In my old Project, this part had an execution from about 0,45 sec, by now I have about 5-6 sec..
I thought about using compiled queries but I recognized these don't support returning IEnumerable yet. Also I tried to avoid Contains() method. But it didn't improve performance anyway.
Could you take short look on my queries and maybe refactor or give some hints how to make one of the queries faster?
It is to note that _repositoryContext.Text has compared to other contexts the most entries (about 50 000), because of translations.
queryNames, queryDefaults, and queryDescriptions are all queries not collections. And you are running them in a loop. Try loading them outside of the loop.
eg: load queryNames to a dictionary:
var queryNames = from text in queryTexts
where !(text.KeyName.EndsWith("$Descr"))
select text;
var queryNamesByName = queryName.ToDictionary(n => n.KeyName);
one can write queries like below
var Profile="developer";
var LstUserName = alreadyUsed.Where(x => x.Profile==Profile).ToList();
you can also use "foreach" like below
lstUserNames.ForEach(x=>
{
//do your stuff
});
In groovy how can i use sql executeQuery method. In my below code i get the error as "Method executeQuery is protected in groovy.sql.Sql" on line 2. Please help!
def sql = new Sql(rdbDsService.getDataSource())
ResultSet rs=sql.executeQuery("select top 5 Id from MACHINES where (Total != Rightcount) order by FinishingTime");
order[0] = 0;
order[1] = 0;
order[2] = 0;
order[3] = 0;
count = 0;
while (rs.next())
{
order[count] = Integer.parseInt(rs["Id"].toString());
count = count + 1;
}
As per the message you're calling a protected method, the javadoc on the method states the following:
Useful helper method which handles resource management when executing
a query which returns a result set. Derived classes of Sql can
override "createQueryCommand" and then call this method to access the
ResultSet returned from the provided query or alternatively can use
the higher-level method of Sql which return result sets which are
funnelled through this method, e.g. eachRow, query.
Instead try using something like eachRow
sql.eachRow("select top 5 Id from MACHINES where (Total != Rightcount) order by FinishingTime") {
order[count] = it.Id
count = count + 1
}
I am using NHibernate.Search libraries in my project for free text search. Recently when I started getting more than 2100 results, I started getting max parameter length error from SQL Server.
Does NHibernate.Search take care of such situation ? Any workaround anyone ?
You could modify NHibernate.Search code to take care of this, or, use custom paging, IE get number of hits for your search, then page nhibernate search results accordingly.
public IList<TEntity> Search<TEntity>(Query query, bool? active, string orderBy)
{
var search = NHibernate.Search.Search.CreateFullTextSession(this.session);
var total = search.CreateFullTextQuery(query, typeof(TEntity)).ResultSize;
var first = 0;
var l = new List<TEntity>();
while (total > 0)
{
l.AddRange(search.CreateFullTextQuery(query, typeof(TEntity))
.SetFirstResult(first)
.SetMaxResults(1000)
.List<TEntity>());
first += 1000;
total -= 1000;
}
return l;
}
See : IFullTextQuery - exception if there are too may objects
I have a query that looks like this:
IQueryable<Profile> profiles = from p in connection.Profiles
where profile.Email.Contains(txtSearch)
select p;
I know that when this is converted to SQL it uses a LIKE '%<value of txtSearch>%' but if txtSearch = "jon%gmail.com" it converts it to `LIKE '%jon~%gmail.com%'. The ~ escapes the % in the middle that is a wild card. How do I get around that? I need to be able to put wild cards into my LINQ to EF searches.
I'm not sure that this is possible directly with linq because you can call only basic string functions like Contains, StartsWith or EndsWith. It is possible with Entity SQL so you can combine these approaches.
var query = new ObjectQuery<Profile>(
#"SELECT VALUE p
FROM CsdlContainerName.Profiles AS p
WHERE p.Email LIKE '" + wildcardSearch + "'",
context);
var result = query.AsQueryable().OrderByDescending(p => p.Name).ToList();
ESQL injection strikes back :)
Second version without injection vulnerability (I didn't try it but it should work):
var commandText =
#"SELECT VALUE p
FROM CsdlContainerName.Profiles AS p
WHERE p.Email LIKE #search";
var query = new ObjectQuery<Profile>(commandText, context);
query.Parameters.Add(new ObjectParameter("search", wildcardSearch));
var result = query.AsQueryable().OrderByDescending(p => p.Name).ToList();
I´m using the LinqDataSource to populate a grid. But now I need the SQL query that the LinqDataSource generates, to pass around throught methods (no, I can't modify the methods to not need a SQL query).
Is there a way to obtain the generated SQL query from a instantiated and configured LinqDataSource?
Hope this helps.
using the function below will return a SqlQueryText
you can rebuild the query from that object.
to get the sql text you can use use the .Text Property
to get the passed
parameters you can use the .Params property
public static SqlQueryText GetFullQueryInfo(DataContext dataContext, IQueryable query)
{
DbCommand dbCommand = dataContext.GetCommand(query);
var result = new SqlQueryText();
result.Text = dbCommand.CommandText;
int nParams = dbCommand.Parameters.Count;
result.Params = new ParameterText[nParams];
for (int j = 0; j < nParams; j++)
{
var param = new ParameterText();
DbParameter pInfo = dbCommand.Parameters[j];
param.Name = pInfo.ParameterName;
param.SqlType = pInfo.DbType.ToString();
object paramValue = pInfo.Value;
if (paramValue == null)
{
param.Value = null;
}
else
{
param.Value = pInfo.Value.ToString();
}
result.Params[j] = param;
}
return result;
}
here is an example
var results = db.Medias.Where(somepredicatehere);
ClassThatHasThisMethod.GetFullQueryInfo(yourdatacontexthere, results);
EDIT:
Sorry forgot to include the SqlQueryText data structures
public struct SqlQueryText
{
public ParameterText[] Params;
public string Text;
}
public struct ParameterText
{
public string Name;
public string SqlType;
public string Value;
}
You can run SQL Profiler while running your application and that should give it to you.
Take a look at LinqPad for debugging and to understand how it works. But if you want it at run-time, I think you're out of luck.
The Sql will only be generated by the Linq to Sql infrastructure at runtime.
I think there are some tools to see generated Sql in the debugger, but if you don't plan to use linq to generate your Sql dynamicaly, shouldn't you probably look for a simple Sql designer ?
I Found a Linq To Sql Debug visualizer on Scottgu's blog.