There are many tables in the database that are used as "lookup" tables. All the tables have the same structure, other than the ID column name.
I have found that I can use reflection to open a table and enumerate through the records. The method takes a string (tableName).
Uri serviceUri = new Uri("http://localhost/MyDataService/WcfDataService.svc");
var context = new MyEntities(serviceUri);
var eTable = typeof(MyEntities).GetProperty(tableName).GetValue(context, null) as IEnumerable<object>
foreach (object o in eTable)
...
This works fine, but I want to add a WHERE clause to the query. For example, where InactiveDate == null.
Can I do this? I have been unable to figure this one out.
How about this?
var eTable = (typeof(MyEntities).GetProperty(tableName).GetValue(context, null) as IEnumerable<object>).Where(obj => obj.GetType().GetProperty("InactiveDate").GetValue(obj) == null);
foreach (object o in eTable)
I would suggest to use generics and maybe an interface over reflection.
public function Xyz<TEntity>(Func<MyEntities, IDbSet<TEntity>> dbSetGetter, Expression<Func<TEntity, Boolean>> filter)
{
var serviceUri = new Uri("http://localhost/MyDataService/WcfDataService.svc");
using (var context = new MyEntities(serviceUri))
{
foreach (var entity in dbSetGetter(context).Where(filter))
{
DoSomethingWith(entity);
}
}
}
Usage would be like this
Xyz(context => context.Foo, foo => foo.Bar == 42);
assuming you have an entity Foo with an integer property Bar. The obvious difference to your code is that you have to know the entity type a compile time and I am not sure if you know it then.
Using Linq commands and Linq To SQL datacontext, Im trying to instance an Entity called "Produccion" from my datacontext in this way:
Demo.View.Data.PRODUCCION pocoProduccion =
(
from m in db.MEDICOXPROMOTORs
join a in db.ATENCIONs on m.cmp equals a.cmp
join e in db.EXAMENXATENCIONs on a.numeroatencion equals e.numeroatencion
join c in db.CITAs on e.numerocita equals c.numerocita
where e.codigo == codigoExamenxAtencion
select new Demo.View.Data.PRODUCCION
{
cmp = a.cmp,
bonificacion = comi,
valorventa = precioEstudio,
codigoestudio = lblCodigoEstudio.Content.ToString(),
codigopaciente = Convert.ToInt32(lblCodigoPaciente.Content.ToString()),
codigoproduccion = Convert.ToInt32(lblNroInforme.Content.ToString()),
codigopromotor = m.codigopromotor,
fecha = Convert.ToDateTime(DateTime.Today.ToShortDateString()),
numeroinforme = Convert.ToInt32(lblNroInforme.Content.ToString()),
revisado = false,
codigozona = (c.codigozona.Value == null ? Convert.ToInt32(c.codigozona) : 0),
codigoclinica = Convert.ToInt32(c.codigoclinica),
codigoclase = e.codigoclase,
}
).FirstOrDefault();
While executing the above code, I'm getting the following error that the stack trace is included:
System.NotSupportedException was caught
Message="The explicit construction of the entity type 'Demo.View.Data.PRODUCCION' in a query is not allowed."
Source="System.Data.Linq"
StackTrace:
en System.Data.Linq.SqlClient.QueryConverter.VisitMemberInit(MemberInitExpression init)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.VisitSelect(Expression sequence, LambdaExpression selector)
en System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.VisitFirst(Expression sequence, LambdaExpression lambda, Boolean isFirst)
en System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc)
en System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node)
en System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node)
en System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression query, SqlNodeAnnotations annotations)
en System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query)
en System.Data.Linq.DataQuery`1.System.Linq.IQueryProvider.Execute[S](Expression expression)
en System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
en Demo.View.InformeMedico.realizarProduccionInforme(Int32 codigoExamenxAtencion, Double precioEstudio, Int32 comi) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 602
en Demo.View.InformeMedico.UpdateEstadoEstudio(Int32 codigo, Char state) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 591
en Demo.View.InformeMedico.btnGuardar_Click(Object sender, RoutedEventArgs e) en D:\cs_InformeMedico\app\InformeMedico.xaml.cs:línea 683
InnerException:
Is that now allowed in LINQ2SQL?
Entities can be created outside of queries and inserted into the data store using a DataContext. You can then retrieve them using queries. However, you can't create entities as part of a query.
I am finding this limitation to be very annoying, and going against the common trend of not using SELECT * in queries.
Still with c# anonymous types there is a workaround, by fetching the objects into an anonymous type, and then copy it over into the correct type.
For example:
var q = from emp in employees where emp.ID !=0
select new {Name = emp.First + " " + emp.Last, EmployeeId = emp.ID }
var r = q.ToList();
List<User> users = new List<User>(r.Select(new User
{
Name = r.Name,
EmployeeId = r.EmployeeId
}));
And in the case when we deal with a single value (as in the situation described in the question) it is even easier, and we just need to copy directly the values:
var q = from emp in employees where emp.ID !=0
select new { Name = emp.First + " " + emp.Last, EmployeeId = emp.ID }
var r = q.FirstOrDefault();
User user = new User { Name = r.Name, EmployeeId = r.ID };
If the name of the properties match the database columns we can do it even simpler in the query, by doing select
var q = from emp in employees where emp.ID !=0
select new { emp.First, emp.Last, emp.ID }
One might go ahead and write a lambda expression that can copy automatically based on the property name, without needing to specify the values explictly.
Here's another workaround:
Make a class that derives from your LINQ to SQL class. I'm assuming that the L2S class that you want to return is Order:
internal class OrderView : Order { }
Now write the query this way:
var query = from o in db.Order
select new OrderView // instead of Order
{
OrderID = o.OrderID,
OrderDate = o.OrderDate,
// etc.
};
Cast the result back into Order, like this:
return query.Cast<Order>().ToList(); // or .FirstOrDefault()
(or use something more sensible, like BLToolkit / LINQ to DB)
Note: I haven't tested to see if tracking works or not; it works to retrieve data, which is what I needed.
I have found that if you do a .ToList() on the query before trying to contruct new objects it works
I just ran into the same issue.
I found a very easy solution.
var a = att as Attachment;
Func<Culture, AttachmentCulture> make =
c => new AttachmentCulture { Culture = c };
var culs = from c in dc.Cultures
let ac = c.AttachmentCultures.SingleOrDefault(
x => x.Attachment == a)
select ac == null ? make(c) : ac;
return culs;
I construct an anonymous type, use IEnumerable (which preserves deferred execution), and then re-consruct the datacontext object. Both Employee and Manager are datacontext objects:
var q = dc.Employees.Where(p => p.IsManager == 1)
.Select(p => new { Id = p.Id, Name = p.Name })
.AsEnumerable()
.Select(item => new Manager() { Id = item.Id, Name = item.Name });
Within the book "70-515 Web Applications Development with Microsoft .NET Framework 4 - Self paced training kit", page 638 has the following example to output results to a strongly typed object:
IEnumerable<User> users = from emp in employees where emp.ID !=0
select new User
{
Name = emp.First + " " + emp.Last,
EmployeeId = emp.ID
}
Mark Pecks advice appears to contradict this book - however, for me this example still displays the above error as well, leaving me somewhat confused. Is this linked to version differences? Any suggestions welcome.
I found another workaround for the problem that even lets you retain your result as IQueryale, so it doesn't actually execute the query until you want it to be executed (like it would with the ToList() method).
So linq doesn't allow you to create an entity as a part of query? You can shift that task to the database itself and create a function that will grab the data you want. After you import the function to your data context, you just need to set the result type to the one you want.
I found out about this when I had to write a piece of code that would produce a IQueryable<T> in which the items don't actually exist in the table containing T.
pbz posted a work around by creating a View class inherited from an entity class that you could be working with. I'm working with a dbml model of a table that has > 200 columns. When I try and return the whole table I get "Root Element missing" errors. I couldn't find anyone who wanted to deal with my particular issue so I was looking at rewriting my entire approach. Just creating a view class for the entitiy class worked in my case.
As pbz suggests : Create a view class that inherits from your entity class. For me this is tbCamp so :
internal class tbCampView : tbCamp
{
}
Then use the view class in your query :
using (var dc = ConnectionClass.Connect(Dev))
{
var camps = dc.tbCamps.Select(s => new tbCampView
{
active = s.active,
idCamp = s.idCamp,
campName = s.campName
});
SmartTableViewer(camps, dg1);
}
private void SmartTableViewer<T>(IEnumerable<T> allRecords)
{
// Build sorted rows back into new table
var table = new DataTable();
// Create columns based on type
if (allRecords is IEnumerable<tbCamp> tbCampRecords)
{
// Get the columns you want
table.Columns.Add("idCamp");
table.Columns.Add("campName");
foreach (var record in tbCampRecords)
{
// Make a new row
var r = table.NewRow();
// Add the contents to each column of the row
r["idCamp"] = record.idCamp;
r["campName"] = record.campName;
// Add the row to the table.
table.Rows.Add(r);
}
}
else
{
MessageBox.Show("Unhandled type. Add support for new data type in SmartTableViewer()");
return;
}
// Update table in grid
dg1.DataSource = table.DefaultView;
}
Here is what happens when you try and create an entity class object in the query.
I didn't want to have to use an anonymous type if I could help it because I wanted the type to be tbCamp. Since tbCampView is of type tbCamp the is operator works well. see Brian Hasden's answer Passing a generic List<> in C#
I'm surprised this is even an issue but with larger tables I run into this error so I thought I would just show it here :
When trying to read this table into memory I get the following error. There are < 2000 rows but the columns are > 200 for each. I don't know if that is an issue or not.
If I just want a few columns I need to create a custom class and handle that which isn't that big of a pain. With the approach pbz provided I don't have to worry about it.
Here is the entire project in case it helps someone.
public partial class Form1 : Form
{
private const bool Dev = true;
public Form1()
{
InitializeComponent();
}
private void btnGetAllCamps_Click(object sender, EventArgs e)
{
using (var dc = ConnectionClass.Connect(Dev))
{
IQueryable<tbCampView> camps = dc.tbCamps.Select(s => new tbCampView
{
// Project columns as needed.
active = s.active,
idCamp = s.idCamp,
campName = s.campName
});
// pass in as a
SmartTableViewer(camps);
}
}
private void SmartTableViewer<T>(IEnumerable<T> allRecords)
{
// Build sorted rows back into new table
var table = new DataTable();
// Create columns based on type
if (allRecords is IEnumerable<tbCamp> tbCampRecords)
{
// Get the columns you want
table.Columns.Add("idCamp");
table.Columns.Add("campName");
foreach (var record in tbCampRecords)
{
//var newRecord = record;
// Make a new row
var r = table.NewRow();
// Add the contents to each column of the row
r["idCamp"] = record.idCamp;
r["campName"] = record.campName;
// Add the row to the table.
table.Rows.Add(r);
}
}
else
{
MessageBox.Show("Unhandled type. Add support for new data type in SmartTableViewer()");
return;
}
// Update table in grid
dg1.DataSource = table.DefaultView;
}
internal class tbCampView : tbCamp
{
}
}
I'm breaking my head with this and decided to share my problem with you
I want to create an anonymous select from several tables, some of them may contain more than one result. i want to concatenate these results into one string
i did something like this:
var resultTable = from item in dc.table
select new
{
id= item.id,
name= CreateString((from name in item.Ref_Items_Names
select name.Name).ToList()),
};
and the CreateString() is:
private string CreateString(List<string> list)
{
StringBuilder stringedData = new StringBuilder();
for (int i = 0; i < list.Count; i++)
{
stringedData.Append(list[i] + ", ");
}
return stringedData.ToString();
}
my intentions were to convert the "name" query to list and then sent it to CreateString() to convert it to one long concatenated string.
I tried using .Aggregate((current,next) => current + "," + next);
but when i try to convert my query to DataTable like below:
public DataTable ToDataTable(Object query)
{
DataTable dt = new DataTable();
IDbCommand cmd = dc.GetCommand(query as IQueryable);
SqlDataAdapter adapter = new SqlDataAdapter();
adapter.SelectCommand = (SqlCommand)cmd;
cmd.Connection.Open();
adapter.Fill(dt);
cmd.Connection.Close();
return dt;
}
I'm getting exception that "dc.GetCommand()" can't understand query with Aggregate method
later I tried to even use this simple query:
var resultTable = from itemin dc.table
select new
{
name = CreateString()
};
When CreateString() returns "success", nothing was inserted to "name"
why there is no way of using methods in select clause?
Thank you
Yotam
There is difference between LINQ to objects and LINQ to some-db-provider. Generally speaking, when using IQueryable, you can't use any methods, except the ones your provider understands.
What you can do is to retrieve the data from the database and then do the formatting using LINQ to objects:
var data = from item in dc.table
where /* some condition */
select item;
var result = from item in data.AsEnumerable()
select new
{
name = SomeFunction(item)
}
The AsEnumerable() extension method forces processing using LINQ to objects.
Forgive me if I've miss interpreted your question. It seems that what you are trying to do is abstract your select method for reuse. If this is the case, you may consider projection using a lambda expression. For example:
internal static class MyProjectors
{
internal static Expression<Func<Object1, ReturnObject>> StringDataProjector
{
get
{
return d => new Object1()
{
//assignment here
}
}
}
}
Now you can select your datasets as such:
dc.Table.Select(MyProjectors.StringDataProjector)
As for the concatenation logic, what about selecting to some base class with an IEnumerable<string> property and a read-only property to handle the concatenation of the string?
Is it possible to apply a WHERE clause on a SubSonic query?
For example, I get get a single based on id...
db.Single<Storage>(id);
But how can I get a single based on a simple WHERE clause?
db.Single<Storage>(WHERE columnname == "value");
that's possible:
// Will return a Storage instance with property IsNew = true, if record does not exist
// since an object created with new never can be null
var storage1 = new Storage(1); // id = 1
var storage1 = new Storage(Storag.Columns.ColumnName, "value");
// Will return 0 if record not found (subsonic3 only)
var storage3 = (from s in Storage
where s.ColumnName == "value"
select s).SingleOrDefault();
// Will throw an exception if record not found (subsonic3 only)
var storage3 = (from s in Storage
where s.ColumnName == "value"
select s).Single();
Since db is a partial class you can extend it. Just create a new File within the same namespace (but another folder in your solution). This applies to subsonic 2 but will be similar to subsonic 3, I think.
public static partial class DB
{
public static T Single<T>(String columName, Object columnValue) where T: RecordBase<T>, new()
{
return Select().From<T>()
.Where(columnName).IsEqualTo(columnValue)
.ExecuteSingle<T>();
}
}
Thanks for the above, this was a help and eventually I simplified this to the below...
db.Single<Storage>(s => s.ColumnName == "value");
So I'm new to linq so be warned what I'm doing may be completely stupid!
I've got a table of caseStudies and a table of Services with a many to many relasionship
the case studies already exist and I'm trying to insert a service whilst linking some case studies that already exist to it. I was presuming something like this would work?
Service service = new Service()
{
CreateDate = DateTime.Now,
CreatedBy = (from u in db.Users
where u.Id == userId
select u).Take(1).First(),
Description = description,
Title = title,
CaseStudies = (from c in db.CaseStudies
where c.Name == caseStudy
select c),
Icon = iconFile,
FeatureImageGroupId = imgGroupId,
UpdateDate = DateTime.Now,
UpdatedBy = (from u in db.Users
where u.Id == userId
select u).Take(1).First()
};
But This isn't correct as it complains about
Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Data.Objects.DataClasses.EntityCollection'
Can somebody please show me the correct way.
Thanks in advance
Yo have to add the query result to the case studies collection instead of trying to replace it.
var service = new Service { ... };
foreach (var caseStudy in db.CaseStudies.Where(s => s.Name == caseStudyName)
{
service.CaseStudies.Add(caseStudy);
}
You can wrap this in an extension method and get a nice syntax.
public static class ExtensionMethods
{
public static void AddRange<T>(this EntityCollection<T> entityCollection,
IEnumerable<T> entities)
{
// Add sanity checks here.
foreach (T entity in entities)
{
entityCollection.Add(entity);
}
}
}
And now you get the following.
var service = new Service { ... };
service.CaseStudies.AddRange(db.CaseStudies.Where(s => s.Name == caseStudyName));