I am using the latest Nhibernate and i have a linq query to return just 1 column. so I can't use for example IQueryable as there is no entity class - i am returning only 1 column. But return to IQueryable Non Generic version doesn't provide the ToList method
Here is the method
public IQueryable GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select new
{
Group = c.Code
}).Distinct();
}
}
Of course if i do this (see below) i get the ToList method on my IQueryable
public IQueryable<Client> GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select c;
}
}
The problem being is that i need to do DISTINCT and use only 1 column.
Any ideas, i am at a loss
Thanks in advance
EDIT
When i look at the type that is returned via IQueryable it is
{NHibernate.Linq.NhQueryable<<>f__AnonymousType6>}
and looking under the base class of what is returned i see an exception
Expression type 10005 is not supported by this SelectClauseVisitor.
Wouldn't the following work?
public IQueryable<X> GetCode() // X = the type of Client.Code
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select c.Code).Distinct();
}
}
The problem here is not just that you can't call ToList on a non-generic IQueryable, but that the entire result is untyped, so you cannot read the Code property of each element either. (This can be worked around with C# 4's dynamic type, but that's not really what you want here.)
In your case, I don't see why you really need to construct an anonymous type just to return a distinct sequence of Code values renamed as Group. Returning the field's value should be sufficient.
If you'd need to return more than just one column, you should create an explicit type, rather than using an anonymous type, so you can say
public IQueryable<ClientGroupAndSomething> GetCode()
{
using (ITransaction transaction = _session.BeginTransaction())
{
var results = (from c in _session.Query<Client>()
select new ClientGroupAndSomething
{
Group = c.Code,
...
}).Distinct();
}
}
Related
I am using the repository pattern with Entity Framework as described in this article: repository pattern with Entity Framework
In the part where the GenericRepository is described (Generic Repository) there is a method which is used to get entities from the database set called Get. It has an orderBy but no groupBy. I am wondering how one might implement a groupBy in the same manner as the orderBy so that you can specify which field to group by dynamically on the entity.
What I have come up with is this:
Func<IQueryable<TEntity>, IGrouping<string, TEntity>> groupBy = null
and then in the method code it should be used something like this:
if(groupBy != null)
{
query = groupBy(query).ToList();
}
But this is not compiling since the IGrouping is not queryable. Does someone know how to point me in the right direction or has a solution to this?
Edit: The reason for doing this instead of using groupby on the returned list is for performance reasons. I want the groupby to be sent as an sql statement to the database and resolved there.
Grouping has no sense without projection. So you have to define new method which returns IEnumerable with new type.
I have added sample of such method. Also removed includeProperties because EF Core ignores Includes during grouping.
Usage sample:
_orderRepostory
.GetGrouped(e => e.UserId, g => new { UserId = g.Key, Count = g.Count()});
And implementation:
public class GenericRepository<TEntity> where TEntity : class
{
... // other code
public virtual IEnumerable<TResult> GetGrouped<TKey, TResult>(
Expression<Func<TEntity, TKey>> groupingKey,
Expression<Func<IGrouping<TKey, TEntity>, TResult>> resultSelector,
Expression<Func<TEntity, bool>>? filter = null)
{
var query = dbSet.AsQueryable();
if (filter != null)
{
query = query.Where(filter);
}
return query.GroupBy(groupingKey).Select(resultSelector);
}
}
I have a function inside a class that will run a Linq to Entities query (or any type of Linq query actually), and it's gonna return 2 columns in the resultset. I would like to return an object to whoever is calling my function that will allow Intellisense to know what I have returned.
Let me explain. If I have a function like this:
public static IQueryable GetInfo(MyEntityModel oEntityModel)
{
var query =
(from t in oEntityModel.Table1
from u in t.Table2
where t.Status == true &&
u.Status == true
select new
{
t.Column1,
u.Column2
})
return query;
}
What can (should) I put instead of IQueryable so that whoever calls my GetInfo function, will get Intellisense from the resultset, and show that it has a Column1 and Column2?
var linqresult = ClsLinqTeste.GetInfo(oEntityModel);
if (linqresult.Column1 == 1)
{
foreach (var oItem in linqresult)
{
.. do stuff...
}
}
Tks
You cannot return an anonymous type from a function, they are strictly "inline" classes. When you return it, the foreach loop will only be able to interpret the result as an plain object. I guess you could use reflection to query the property names and values, however it seems much more straight forward to define a data transfer type to hold the results.
See this question, and this blog post.
So you could create a simple struct or class:
public class MyDataResult
{
public object Column1 { get; set; }
public object Column2 { get; set; }
}
Then modify your query in the function:
public static IQueryable<MyDataResult> GetInfo(MyEntityModel oEntityModel)
{
var query =
(from t in oEntityModel.Table1
from u in t.Table2
where t.Status == true &&
u.Status == true
select new MyDataResult
{
Column1 = t.Column1,
Column2 = u.Column2
})
return query;
}
Something like that should work. Note that I used "object" for the properties in MyDataResult. I don't know the types of the columns you are returning, you should use the actual types in order to get full intellisense.
You are returning a collection of anonymous types, they will be casted to objects, so when you try to iterate over them, altough they will be your objects (and they will contain your properties) at compile time they will be casted to objects:
foreach (var x in ClsLinqTeste.GetInfo(oEntityModel))
{
//x is an Object
}
You can read more about it here.
If you want to have intellisense, I suggest you create a custom class they will hold your properties and return not an anonymous type (using new {}) but object of your class (new MyClass(prop1, prop2)). You also need to change signature of your method, so it returns IQueryable<YourClass> and not just plain non-generic IQueryable.
As others have said, creating a new type to hold the two columns is usually the best option.
But if, for some reason, you don't want to do that and you are using .Net 4.0, you can use Tuple:
public static IQueryable<Tuple<Column1Type, Column2Type>>
GetInfo(MyEntityModel oEntityModel)
{
return from …
select Tuple.Create(t.Column1, u.Column2);
}
var linqresult = ClsLinqTeste.GetInfo(oEntityModel);
foreach (var oItem in linqresult)
Console.WriteLIne(oItem.Item1, oItem.Item2);
When you return your resultset AsQueryable, the app is already able to give you intellisense, however in your example, you must specify either .FirstOrDefault if you know your collection will only have a single row, or iterate over your collection to get the items from it, like so:
This is what you're doing:
var linqresult = ClsLinqTeste.GetInfo(oEntityModel);
if (linqresult.Column1 == 1)
{
..do stuff...
}
This is how you should do it:
var linqresult = ClsLinqTeste.GetInfo(oEntityModel);
foreach(var item in linqresult)
{
if (item.Column1 == 1)
{
..do stuff...
}
}
You must iterate over linqresult because when you query with link, it returns a result set, even if it just has one column. As with any collection, your data columns aren't available on the whole result set, only with individual items.
If you want to strongly typed enumerate a non-generic IEnumerable (IEnumerable.GetEnumerator() instead of IEnumerable<T>.GetEnumerator<T>()) you can use the Cast<>() extension, like so
var myquery = GetQueryable();
for (var item in myquery.Cast<MyDataType>())
{
// use item.Column1 directly and strongly typed with intellisense
}
I have IQueryable object and I need to take the data inside the IQueryable to put it into Textboxs controls. Is this possible?
I try something like:
public void setdata (IQueryable mydata)
{
textbox1.text = mydata.????
}
Update:
I'm doing this:
public IQueryable getData(String tableName, Hashtable myparams)
{
decimal id = 0;
if (myparams.ContainsKey("id") == true)
id = (decimal)myparams["id"];
Type myType= Type.GetType("ORM_Linq." + tableName + ", ORM_Linq");
return this.GetTable(tableName , "select * from Articu where id_tipo_p = '" + id + "'");
}
public IQueryable<T> GetTable<T>(System.Linq.Expressions.Expression<Func<T, bool>> predicate) where T : class
{
return _datacontext.GetTable<T>().Where(predicate);
}
This returns a {System.Data.Linq.SqlClient.SqlProvider+OneTimeEnumerable1[ORM_Linq.Articu]}`
I don't see any method like you tell me. I see Cast<>, Expression, ToString...
EDIT: Updated based on additional info from your other posts...
Your getData method is returning IQueryable instead of a strongly typed result, which is why you end up casting it. Try changing it to:
public IQueryable<ORM_Linq.Articu> getData(...)
Are you trying to query for "Articu" from different tables?
With the above change in place, your code can be rewritten as follows:
ORM_Linq.Articu result = mydata.SingleOrDefault();
if (result != null)
{
TextBoxCode.Text = result.id.ToString();
TextBoxName.Text = result.descrip;
}
If you have a single result use SingleOrDefault which will return a default value if no results are returned:
var result = mydata.SingleOrDefault();
if (result != null)
{
textbox1.text = result.ProductName; // use the column name
}
else
{
// do something
}
If you have multiple results then loop over them:
foreach (var item in mydata)
{
string name = item.ProductName;
int id = item.ProductId;
// etc..
}
First, you should be using a strongly-typed version of IQueryable. Say that your objects are of type MyObject and that MyObject has a property called Name of type string. Then, first change the parameter mydata to be of type IQueryable<MyObject>:
public void setdata (IQueryable<MyObject> mydata)
Then we can write a body like so to actually get some data out of. Let's say that we just want the first result from the query:
public void setdata (IQueryable<MyObject> mydata) {
MyObject first = mydata.FirstOrDefault();
if(first != null) {
textbox1.Text = first.Name;
}
}
Or, if you want to concatenate all the names:
public void setdata(IQueryable<MyObject> mydata) {
string text = String.Join(", ", mydata.Select(x => x.Name).ToArray());
textbo1.Text = text;
}
Well, as the name suggests, an object implementing IQueryable is... Queryable! You'll need to write a linq query to get at the internal details of your IQueryable object. In your linq query you'll be able to pull out its data and assign bits of it where ever you'd like - like your text box.
Here's a great starting place for learning Linq.
I think you find the same mental struggle when coming from FoxPro and from DataSet. Really nice, powerful string-based capabilities(sql for query, access to tables and columns name) in these worlds are not available, but replaced with a compiled, strongly-typed set of capabilities.
This is very nice if you are statically defining the UI for search and results display against a data source known at compile time. Not so nice if you are trying to build a system which attaches to existing data sources known only at runtime and defined by configuration data.
If you expect only one value just call FirstOrDefault() method.
public void setdata (IQueryable mydata)
{
textbox1.text = mydata.FirstOrDefault().PropertyName;
}
How do you query a collection which is populated/created with select new?
I have this BindingSource:
this.bindingSource.DataSource =
from row in db.Table
select new
{
name = row.Name + row.Num.ToString()
};
I'd like to query it like I do with other BindingSources:
var query = from row in (IEnumerable<Table>)anotherBindingSource.List
where row.name == "asd"
select row;
Since bindingSource contains anonymous types I get this error:
Unable to cast object of type
'System.Data.Linq.SortableBindingList1[<>f__AnonymousType815
etc. etc. to type 'System.Collections.Generic.IEnumerable`1[Table]'.
What should I do?
Well, not sure exactly what you're trying to do here, but an anonymous type != a Table object. The exception indicates you're trying to cast an IEnum of an anonymous type (a compiler-generated class with a weird name) to an IEnum of type Table.
You can't cast types willy nilly in C#. You can't, for instance, do this:
(Table)"Lol I'd like to be a table pls kthx"
You can't cast any type that isn't already a Table, or extends from Table, to a Table.
So what you're asking is impossible. You should probably take a step back and ask a more general question about what you're trying to accomplish.
Some more on anon types... They only really have meaning within the scope of the method in which they are defined. It appears you might be returning your anon type enumeration from a method call and then are attempting to sort. This won't work, as once the anonymous type leaves the method scope it is considered (at least by intellisense) to be an object and the only way to get at its properties is to use reflection.
If your example isn't just a simplified version, you could just skip the anon type altogether...
this.bindingSource.DataSource =
from row in db.Table
select row.Name + row.Num.ToString();
This is an IEnumerable, and can be queried thusly:
var query = from row in anotherBindingSource
where row.StartsWith("asd")
select row;
However it doesn't look like you're accomplishing much at all with this...
You cannot query anonymous types outside of the scope in which they are defined.
This works:
public void Worthless(Hurr hurr)
{
var query = from x in hurr select new { x.Durr };
var requery = from x in query where x.Durr == "lol" select x;
}
This does not:
public class Anonymous
{
public IEnumerable GetMyDurrs(Hurr hurr)
{
return from x in Hurr select new { x.Durr };
}
public IEnumerable WeedMyDurrs(Hurr hurr, string value)
{
// this won't compile
return from x in GetMyDurrs(hurr) where x.Durr == value select x;
}
}
The second example won't compile because the anonymous type was defined within another scope.
The only way to get this to work is to define a type.
public class Anonymous
{
public IEnumerable<Anonymous.MyDurr> GetMyDurrs(Hurr hurr)
{
return from x in Hurr select new MyDurr { Durr = x.Durr };
}
public IEnumerable<Anonymous.MyDurr> WeedMyDurrs(Hurr hurr, string value)
{
// this won't compile
return from x in GetMyDurrs(hurr) where x.Durr == value select x;
}
public class MyDurr { public string Durr {get;set;} }
}
If I have something like:
var query = from children in _data.Children
where children.ChildId == childId
select new CustomModel.MyChild
{
ChildId = children.ChildId,
Name = children.ChildName
};
return query.FirstOrDefault();
Where I want the resultant object to be my custom model.
Can I handle the custom model instantiation in a different method, which could be reused if I had multiple linq queries that all generated a custom child model?
For example,
var query = from children in _data.Children
where children.ChildId == childId
select CreateMyCustomChild([param ??]);
return query.FirstOrDefault();
This may well be impossible, I don't know, but what would the method signature be like if it is possible?
I'm only thinking reuse for when multiple linq queries contain duplicate object initialisation code.
Thanks
It really depends on what version of LINQ you're using. If you're using LINQ to SQL, I don't believe you can call arbitrary methods in the query. The query translator wouldn't know what to do with the method call
If you're using LINQ to Objects, you're absolutely fine to do it, like this:
var query = from children in _data.Children
where children.ChildId == childId
select CreateMyCustomChild(children)
return query.FirstOrDefault();
// Elsewhere
public CustomModel.MyChild CreateMyCustomChild(OtherChild child)
{
return new CustomModel.MyChild
{
ChildId = child.ChildId,
Name = child.ChildName
};
}
(Side note: I'd call the range variable in the query "child" rather than "children" as at any one time it only represents a single child.)
If you wanted you could write "select 1" or in your case "CreateMyCustomChild(children)" since "children" is containing all your info. In your case you aren't adding a lot of info to "children", so why not "select children"?
In other words, just try it out. The return type of your value will determine over which type your LINQ enumerates.
Suppose you had a method that did the transform for you.
public static class Conversions
{
public static CustomModel.MyChild ToCustomModel(this DataModel.MyChild source)
{
return new CustomModel.MyChild()
{
ChildId = source.ChildId,
Name = source.ChildName
}
}
}
You can use such a method to do the conversion of a single item.
DataModel.MyChild myResult = getResult();
CustomModel.MyChild myConvertedResult = myResult.ToCustomModel()
Such a method can also be used in a Enumerable.Select method call.
IEnumerable<DataModel.MyChild> myQueriedResults = getResult();
IEnumerable<CustomModel.MyChild> myConvertedResults =
myQueryiedResults.Select(c => c.ToCustomModel());
While you can do with expressions, I don't think it is worth the hassle. Instead I suggest you define an extension method like:
IQueryable<CustomModel.MyChild> ToModel(this IQueryable<Child> childs)
{
return childs.Select( c=>
select new CustomModel.MyChild
{
ChildId = children.ChildId,
Name = children.ChildName
}
);
}
You can then call:
return _data.Children
.Where(c=>c.ChildId == childId)
.ToModel()
.FirstOrDefault();