I have queries that are built like this:
public static List<MyObjectModel> GetData (int MyParam)
{
using (DataModel MyModelDC = new DataModel())
{ var MyQuery = from....
select MyObjectModel { ...}
}
return new List<MyObjectModel> (MyQuery)
}
}
It seems that using compiled linq-to-sql queries are about as fast as stored procedures and so the goal is to convert these queries into compiled queries. What's the syntax for this?
Thanks.
Put something like this inside of your DataContext (or in your case your "DataModel"):
private static Func<DataModel, int, MyObjectModel> _getObjectModelById =
CompiledQuery.Compile<DataModel, int, MyObjectModel>(
(dataModel, myParam) =>
dataModel.PersonDtos.where(c => c.ObjectModelId == myParam).FirstOrDefault()
);
Then add amethod in there to call it like this:
internal List<MyObjectModel> GetObjectModel(int myParam)
{
var results = _getObjectModelById(this, myParam);
return results.SingleOrDefault();
}
Inside of your repository where your original method was call the internal function to get the result you are looking for.
Hope this helps -> I can post more code if necessary :)
Related
READ EDIT
I have a similar implementation to AsyncCrudAppService related to filtering queries. When I run tests on top of ABPs implementation of Application Services derived of AsyncCrudAppServiceBase, everything runs fine. When I do the same running on top of my custom "filters", I get the following error:
System.ObjectDisposedException : Cannot access a disposed object [...]
Object name: 'DataManagerDbContext'.
I know the solution is using IUnitOfWorkManager and calling Begin() method to define a UnitOfWork, but since I am working with AppServices, I thought there was already a UnitOfWork defined. These are my methods:
public PagedResultDto<StateDetails> GetEditorList(EditorRequestDto input)
{
var query = _stateRepository.GetAllIncluding(p => p.Country).AsQueryable();
query = ApplySupervisorFilter(query);
query = query.ApplyFiltering(input, "Name");
var totalCount = query.Count();
query = query.ApplySorting<State, int, PagedAndSortedResultRequestDto>(input);
query = query.ApplyPaging<State, int, PagedAndSortedResultRequestDto>(input);
var entities = query.ToList();
return new PagedResultDto<StateDetails>(totalCount, ObjectMapper.Map<List<StateDetails>>(entities));
}
private IQueryable<State> ApplySupervisorFilter(IQueryable<State> query)
{
if (!SettingManager.GetSettingValue<bool>(AppSettingNames.SupervisorFlag))
{
query = ApplyUncategorizedFilter(query);
}
return query;
}
private IQueryable<State> ApplyUncategorizedFilter(IQueryable<State> query)
{
return query.Where(
p => !p.CountryId.HasValue);
}
My passing test (with manual UnitOfWork):
[Fact]
public async Task GetEditorListWithouSupervisorFlag_Test()
{
using (UnitOfWorkManager.Begin())
{
await ChangeSupervisorFlag(false);
var result = _stateAppService.GetEditorList(
new EditorRequestDto
{
MaxResultCount = 10,
});
result.Items.Any(p => p.Country == null).ShouldBe(true);
}
}
Does anybody know an solution to this "issue"? It would be annoying to define a UnitOfWork for every test I perform. It also seems like I am doing something wrong
EDIT
I have solved the issue. I must use an interface for my Application Service when running tests so it is able to mock it properly
I have solved the issue. I must use an interface for my Application Service when running tests so it is able to mock it properly
I am in the middle of a refactoring cycle where I converted some extension methods that used to look like this:
public static IQueryable<Family> FilterOnRoute(this IQueryable<Family> families, WicRoute route)
{
return families.Where(fam => fam.PODs
.Any(pod => pod.Route.RouteID == route.RouteID));
}
to a more fluent implementation like this:
public class SimplifiedFamilyLinqBuilder
{
private IQueryable<Family> _families;
public SimplifiedFamilyLinqBuilder Load(IQueryable<Family> families)
{
_families = families;
return this;
}
public SimplifiedFamilyLinqBuilder OnRoute(WicRoute route)
{
_families = _families.Where(fam => fam.PODs
.Any(pod => pod.Route.RouteID == route.RouteID));
return this;
}
public IQueryable<Family> AsQueryable()
{
return _families;
}
}
which I can call like this: (note this is using Linq-to-Nhibernate)
var families =
new SimplifiedFamilyLinqBuilder()
.Load(session.Query<Family>())
.OnRoute(new WicRoute() {RouteID = 1})
.AsQueryable()
.ToList();
this produces the following SQL which is fine with me at the moment: (of note is that the above Linq is being translated to a SQL Query)
select ... from "Family" family0_
where exists (select pods1_.PODID from "POD" pods1_
inner join Route wicroute2_ on pods1_.RouteID=wicroute2_.RouteID
where family0_.FamilyID=pods1_.FamilyID
and wicroute2_.RouteID=#p0);
#p0 = 1
my next effort in refactoring is to move the query part that deals with the child to another class like this:
public class SimplifiedPODLinqBuilder
{
private IQueryable<POD> _pods;
public SimplifiedPODLinqBuilder Load(IQueryable<POD> pods)
{
_pods = pods;
return this;
}
public SimplifiedPODLinqBuilder OnRoute(WicRoute route)
{
_pods = _pods.Where(pod => pod.Route.RouteID == route.RouteID);
return this;
}
public IQueryable<POD> AsQueryable()
{
return _pods;
}
}
with SimplifiedFamilyLinqBuilder changing to this:
public SimplifiedFamilyLinqBuilder OnRoute(WicRoute route)
{
_families = _families.Where(fam =>
_podLinqBuilder.Load(fam.PODs.AsQueryable())
.OnRoute(route)
.AsQueryable()
.Any()
);
return this;
}
only I now get this error:
Remotion.Linq.Parsing.ParserException : Cannot parse expression 'value(Wic.DataTests.LinqBuilders.SimplifiedPODLinqBuilder)' as it has an unsupported type. Only query sources (that is, expressions that implement IEnumerable) and query operators can be parsed.
I started to implement IQueryable on SimplifiedPODLinqBuilder(as that seemed more logical than implementing IEnumberable) and thought I would be clever by doing this:
public class SimplifiedPODLinqBuilder : IQueryable
{
private IQueryable<POD> _pods;
...
public IEnumerator GetEnumerator()
{
return _pods.GetEnumerator();
}
public Expression Expression
{
get { return _pods.Expression; }
}
public Type ElementType
{
get { return _pods.ElementType; }
}
public IQueryProvider Provider
{
get { return _pods.Provider; }
}
}
only to get this exception (apparently Load is not being called and _pods is null):
System.NullReferenceException : Object reference not set to an instance of an object.
is there a way for me to refactor this code out that will parse properly into an expression that will go to SQL?
The part fam => _podLinqBuilder.Load(fam.PODs.AsQueryable() is never going to work, because the linq provider will try to parse this into SQL and for that it needs mapped members of Family after the =>, or maybe a mapped user-defined function but I don't know if Linq-to-Nhibernate supports that (I never really worked with it, because I still doubt if it is production-ready).
So, what can you do?
To be honest, I like the extension methods much better. You switched to a stateful approach, which doesn't mix well with the stateless paradigm of linq. So you may consider to retrace your steps.
Another option: the expression in .Any(pod => pod.Route.RouteID == route.RouteID)); could be paremeterized (.Any(podExpression), with
OnRoute(WicRoute route, Expression<Func<POD,bool>> podExpression)
(pseudocode).
Hope this makes any sense.
You need to separate methods you intend to call from expressions you intend to translate.
This is great, you want each of those methods to run. They return an instance that implements IQueryable<Family> and operate on that instance.
var families = new SimplifiedFamilyLinqBuilder()
.Load(session.Query<Family>())
.OnRoute(new WicRoute() {RouteID = 1})
.AsQueryable()
.ToList();
This is no good. you don't want Queryable.Where to get called, you want it to be an expression tree which can be translated to SQL. But PodLinqBuilder.Load is a node in that expression tree which can't be translated to SQL!
families = _families
.Where(fam => _podLinqBuilder.Load(fam.PODs.AsQueryable())
.OnRoute(route)
.AsQueryable()
.Any();
You can't call .Load inside the Where expression (it won't translate to sql).
You can't call .Load outside the Where expression (you don't have the fam parameter).
In the name of "separation of concerns", you are mixing query construction methods with query definition expressions. LINQ, by its Integrated nature, encourages you to attempt this thing which will not work.
Consider making expression construction methods instead of query construction methods.
public static Expression<Func<Pod, bool>> GetOnRouteExpr(WicRoute route)
{
int routeId = route.RouteID;
Expression<Func<Pod, bool>> result = pod => pod.Route.RouteID == route.RouteID;
return result;
}
called by:
Expression<Func<Pod, bool>> onRoute = GetOnRouteExpr(route);
families = _families.Where(fam => fam.PODs.Any(onRoute));
With this approach, the question is now - how do I fluidly hang my ornaments from the expression tree?
Suppose following codes:
IEnumerable<MyClass> MakeQuery()
{
var query = from m in session.Linq<MyClass>()
select m;
return query;
}
List<MyClass> m1()
{
return MakeQuery()
.Skip(10)
.Take(20)
.ToList<MyClass>();
}
List<MyClass> m2()
{
var query = from m in session.Linq<MyClass>()
select m;
return query
.Skip(10)
.Take(20)
.ToList<MyClass>();
}
Supposing all queries are same, it seems that in m1(), Skip and Take does not work. Indeed its like they do not exist all.
Why this happens and how can be fixed?
I'm using linq-to-nhibernate and this methods are used for paging. Thanks.
Why not use IQueryable for the MakeQuery() method?
IQueryable<MyClass> MakeQuery()
{
return session.Linq<MyClass>();
}
Not that the actual query makes a lot of sense. But I'll leave that to you.
But this is also the only difference between m1() and m2()
Forgive me if this has been asked already. I've only just started using LINQ. I have the following Expression:
public static Expression<Func<TblCustomer, CustomerSummary>> SelectToSummary()
{
return m => (new CustomerSummary()
{
ID = m.ID,
CustomerName = m.CustomerName,
LastSalesContact = // This is a Person entity, no idea how to create it
});
}
I want to be able to populate LastSalesContact, which is a Person entity.
The details that I wish to populate come from m.LatestPerson, so how can I map over the fields from m.LatestPerson to LastSalesContact. I want the mapping to be re-useable, i.e. I do not want to do this:
LastSalesContact = new Person()
{
// Etc
}
Can I use a static Expression, such as this:
public static Expression<Func<TblUser, User>> SelectToUser()
{
return x => (new User()
{
// Populate
});
}
UPDATE:
This is what I need to do:
return m => (new CustomerSummary()
{
ID = m.ID,
CustomerName = m.CustomerName,
LastSalesContact = new Person()
{
PersonId = m.LatestPerson.PersonId,
PersonName = m.LatestPerson.PersonName,
Company = new Company()
{
CompanyId = m.LatestPerson.Company.CompanyId,
etc
}
}
});
But I will be re-using the Person() creation in about 10-15 different classes, so I don't want exactly the same code duplicated X amount of times. I'd probably also want to do the same for Company.
Can't you just use automapper for that?
public static Expression<Func<TblCustomer, CustomerSummary>> SelectToSummary()
{
return m => Mapper.Map<TblCustomer, CustommerSummary>(m);
}
You'd have to do some bootstrapping, but then it's very reusable.
UPDATE:
I may not be getting something, but what it the purpose of this function? If you just want to map one or collection of Tbl object to other objects, why have the expression?
You could just have something like this:
var customers = _customerRepository.GetAll(); // returns IEnumerable<TblCustomer>
var summaries = Mapper.Map<IEnumerable<TblCustomer>, IEnumerable<CustomerSummary>>(customers);
Or is there something I missed?
I don't think you'll be able to use a lambda expression to do this... you'll need to build up the expression tree by hand using the factory methods in Expression. It's unlikely to be pleasant, to be honest.
My generally preferred way of working out how to build up expression trees is to start with a simple example of what you want to do written as a lambda expression, and then decompile it. That should show you how the expression tree is built - although the C# compiler gets to use the metadata associated with properties more easily than we can (we have to use Type.GetProperty).
This is always assuming I've understood you correctly... it's quite possible that I haven't.
How about this:
public static Person CreatePerson(TblPerson data)
{
// ...
}
public static Expression<Func<TblPerson, Person>> CreatePersonExpression()
{
return d => CreatePerson(d);
}
return m => (new CustomerSummary()
{
ID = m.ID,
CustomerName = m.CustomerName,
LastSalesContact = CreatePerson(m.LatestPerson)
});
I have a variable size array of strings, and I am trying to programatically loop through the array and match all the rows in a table where the column "Tags" contains at least one of the strings in the array. Here is some pseudo code:
IQueryable<Songs> allSongMatches = musicDb.Songs; // all rows in the table
I can easily query this table filtering on a fixed set of strings, like this:
allSongMatches=allSongMatches.Where(SongsVar => SongsVar.Tags.Contains("foo1") || SongsVar.Tags.Contains("foo2") || SongsVar.Tags.Contains("foo3"));
However, this does not work (I get the following error: "A lambda expression with a statement body cannot be converted to an expression tree")
allSongMatches = allSongMatches.Where(SongsVar =>
{
bool retVal = false;
foreach(string str in strArray)
{
retVal = retVal || SongsVar.Tags.Contains(str);
}
return retVal;
});
Can anybody show me the correct strategy to accomplish this? I am still new to the world of LINQ :-)
You can use the PredicateBuilder class:
var searchPredicate = PredicateBuilder.False<Songs>();
foreach(string str in strArray)
{
var closureVariable = str; // See the link below for the reason
searchPredicate =
searchPredicate.Or(SongsVar => SongsVar.Tags.Contains(closureVariable));
}
var allSongMatches = db.Songs.Where(searchPredicate);
LinqToSql strange behaviour
I recently created an extension method for creating string searches that also allows for OR searches. Blogged about here
I also created it as a nuget package that you can install:
http://www.nuget.org/packages/NinjaNye.SearchExtensions/
Once installed you will be able to do the following
var result = db.Songs.Search(s => s.Tags, strArray);
If you want to create your own version to allow the above, you will need to do the following:
public static class QueryableExtensions
{
public static IQueryable<T> Search<T>(this IQueryable<T> source, Expression<Func<T, string>> stringProperty, params string[] searchTerms)
{
if (!searchTerms.Any())
{
return source;
}
Expression orExpression = null;
foreach (var searchTerm in searchTerms)
{
//Create expression to represent x.[property].Contains(searchTerm)
var searchTermExpression = Expression.Constant(searchTerm);
var containsExpression = BuildContainsExpression(stringProperty, searchTermExpression);
orExpression = BuildOrExpression(orExpression, containsExpression);
}
var completeExpression = Expression.Lambda<Func<T, bool>>(orExpression, stringProperty.Parameters);
return source.Where(completeExpression);
}
private static Expression BuildOrExpression(Expression existingExpression, Expression expressionToAdd)
{
if (existingExpression == null)
{
return expressionToAdd;
}
//Build 'OR' expression for each property
return Expression.OrElse(existingExpression, expressionToAdd);
}
}
Alternatively, take a look at the github project for NinjaNye.SearchExtensions as this has other options and has been refactored somewhat to allow other combinations
There is another, somewhat easier method that will accomplish this. ScottGu's blog details a dynamic linq library that I've found very helpful in the past. Essentially, it generates the query from a string you pass in. Here's a sample of the code you'd write:
Dim Northwind As New NorthwindDataContext
Dim query = Northwind.Products _
.Where("CategoryID=2 AND UnitPrice>3") _
.OrderBy("SupplierId")
Gridview1.DataSource = query
Gridview1.DataBind()
More info can be found at scottgu's blog here.
Either build an Expression<T> yourself, or look at a different route.
Assuming possibleTags is a collection of tags, you can make use of a closure and a join to find matches. This should find any songs with at least one tag in possibleTags:
allSongMatches = allSongMatches.Where(s => (select t from s.Tags
join tt from possibleTags
on t == tt
select t).Count() > 0)