After a gap, again I entered to Visual C++ 2010. Now my intention is to prepare a LINQ Query to select a distinct value from a datatable
In C# My Query
var ProjLnkQry = (from P in MyGlobalData.ProjectTbl.AsEnumerable() select P["proj_name"]).Distinct().ToList();
The above query I try to convert it into VIsual C++
auto DistDepQry=(from v1 in MyGlobalData::ProjectTbl::AsEnumaerable() select v1["depart_name"])->Distinct()->ToList();
But not succeeded....Thanks for the ideas...
Try something like this:
String^ SelectFn(Task^ i) { return i->Name; }
void Fn()
{
List<Task^>^ data = GetData();
List<String^>^ query = Enumerable::ToList(
Enumerable::Distinct(
Enumerable::Select(
Enumerable::AsEnumerable(data),
gcnew Func<Task^, String^>(&SelectFn)
)
)
);
}
Obviously you should change types, to match your query, but I hope that would be enough for start.
Related
I need to filter some Entities by various fields using "normal" WHERE and IN clauses in a query over my database, but I do not know how to do that with EF.
This is the approach:
Database table
Licenses
-------------
license INT
number INT
name VARCHAR
...
desired SQL Query in EF
SELECT * FROM Licenses WHERE license = 1 AND number IN (1,2,3,45,99)
EF Code
using (DatabaseEntities db = new DatabaseEntities ())
{
return db.Licenses.Where(
i => i.license == mylicense
// another filter
).ToList();
}
I have tried with ANY and CONTAINS, but I do not know how to do that with EF.
How to do this query in EF?
int[] ids = new int[]{1,2,3,45,99};
using (DatabaseEntities db = new DatabaseEntities ())
{
return db.Licenses.Where(
i => i.license == mylicense
&& ids.Contains(i.number)
).ToList();
}
should work
I'm trying to the the value of a lookup field in SharePoint using Linq and a collection of SPListItem - something like this:
int totalDepts = (from SPListItem itm in hourEntries select ((SPFieldLookupValue)itm["Level1"]).LookupValue).Distinct().Count();
But that doesn't seem to work (and it strikes me as missing some steps)
Has anyone done this before?
I wasn't able to figure out to do it directly in the Linq query, so I ended up creating WorkHoursEntries object, and populating it with all my SPListItems
List<WorkHourEntry> workHourEntries = new List<WorkHourEntry>();
foreach (SPListItem hourEntry in hourItems)
{
//Collect entries that are in the current Fiscal Year reporting period
if (fiscalYearMonths.Contains(hourEntry["Reporting_x0020_Month"].ToString()))
{
WorkHourEntry curEntry = new WorkHourEntry();
string Level1 = (string)hourEntry["Level1"];
SPFieldLookupValue val = new SPFieldLookupValue(Level1);
curEntry.organization = val.LookupValue;
SPFieldCalculated cf = (SPFieldCalculated)hourEntry.Fields["WECSCHours"];
curEntry.WECSCHours = cf.GetFieldValueForEdit(hourEntry["WECSCHours"]);
workHourEntries.Add(curEntry);
}
}
This allowed me to run Linq queries directly on the WorkHourEntry collection
var uniqueDeptNames = (from itm in workHourEntries select itm.organization).Distinct().ToArray();
It's an exercise of EF code-first. There's a simple method. I want to get the Entity SQL command text generated by object services.
(MyDbContext is derived form DbContext. Person is a POCO class.)
using (MyDbContext context = new MyDbContext())
{
var query = context.Set<Person>().FirstOrDefault(p => p.Age == 1);
Console.WriteLine(query.Name);
var objquery = query as ObjectQuery;
if (objquery != null)
Console.WriteLine(objquery.CommandText);
}
I used to get native SQL command text by ObjectQuery.TraceString in LINQ to Entity. Now, what I need is Entity-SQL statement, NOT native SQL statement.
But, I can't cast the query from IQueryable<Person> to ObjectQuery or ObjectQuery<Person>.
I tried to get members of DbQuery by reflection. It seems that DbQuery hasn't any property about command text or trace string.
Thanks
My suggestion for what you want is using Dynamic Linq. The library (part of the Linq Samples) includes many IQueryable extensions that return Linq.DataQuery objects. Once you consume the DataQuery you'll have the expected object.
var testQuery =
db.Cases.
Where("KeyID > 1").
Take(1);
foreach (var r in testQuery)
{
Console.WriteLine(r);
}
Then, you can check against your query as such.
testQuery.Expression
testQuery.Provider
These will give you:
{Table(Case).Where( => (.Keyid > 1)).Take(1)}
System.Linq.Expressions.Expression {System.Linq.Expressions.MethodCallExpression}
-and-
{SELECT TOP (1) [t0].[Keyid], [t0].[FileNo], [t0].[MatterType], [t0].[LoanNo], [t0].[Investor], [t0].[LoanType], [t0].[Client], [t0].[ClientFileNo], [t0].[ClientStatus], [t0].[Mortgagor], [t0].[County], [t0].[PropertyStreet1], [t0].[PropertyStreet2], [t0].[PropertyCity], [t0].[PropertyState], [t0].[PropertyZipcode], [t0].[Status], [t0].[BoxNo], [t0].[InsurerLoanno], [t0].[InvestorLoanno], [t0].[insurer_name_id], [t0].[OldSystemKey], [t0].[FinalBilling], [t0].[HoldBilling], [t0].[LastModified], [t0].[PiggyLoanNo], [t0].[CurrComentID], [t0].[LockEFILE], [t0].[MSJAmount], [t0].[Created], [t0].[Locked], [t0].[FinalBillingDate], [t0].[HoldBillingDate], [t0].[CreatedBy], [t0].[Stage], [t0].[PriorStage], [t0].[DefendantUpdated], [t0].[VestingCode], [t0].[FileSource], [t0].[SubVestingCode], [t0].[AttorneyAssigment], [t0].[VoluntarySurrender], [t0].[FNMARisk], [t0].[Source], [t0].[REO_ID], [t0].[WTI_ID], [t0].[CaseDismissed], [t0].[REO_CompanyID], [t0].[SubMattertype], [t0].[VendorCode], [t0].[SubType]
FROM [dbo].[Cases] AS [t0]
WHERE [t0].[Keyid] > #p0}
System.Linq.IQueryProvider {System.Data.Linq.DataQuery<CMSDEVMapping.Case>}
You can also verify your type in the loop:
r.GetType() {Name = "Case" FullName = "CMSDEVMapping.Case"} System.Type {System.RuntimeType}
I want to see what my insert statement would look like as if I was wiring
up an text-based ADO.NET command. How do I do this?
I have been following the below link:
http://damieng.com/blog/2008/07/30/linq-to-sql-log-to-debug-window-file-memory-or-multiple-writers
And have added the DebugTextWriter class to my project. So, now, in my code I have the following which doesn't really do anything and I don't think its right:
using(WorkbookDataContext dc = _conn.GetContext())
{
if(profile.ProfileId > 0)
{
dc.Profiles.Attach(profile, true);
}
else
{
dc.Profiles.InsertOnSubmit(profile);
}
dc.Log = new DebugTextWriter();
#if DEBUG
dc.Log = new System.IO.StreamWriter("linq-to-sql.log")
{
AutoFlush = true
};
#endif
dc.SubmitChanges();
}
Any ideas what I am doing wrong and/or how to inspect my LINQ insert statement correctly?
Thanks
How to: Display Generated SQL (LINQ to SQL)
You can view the SQL code with the Log property.
Example: use the Log property to display SQL code in the console window before the code is executed.
You can use this property with query, insert, update & delete commands.
db.Log = Console.Out;
IQueryable<Customer> custQuery =
from cust in db.Customers
where cust.City == "London"
select cust;
foreach(Customer custObj in custQuery)
{
Console.WriteLine(custObj.CustomerID);
}
These lines from the console window are what you see when you execute the C# code above.
SELECT [t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName], [t0].[ContactT
itle], [t0].[Address], [t0].[City], [t0].[Region], [t0].[PostalCode], [t0].[Coun
try], [t0].[Phone], [t0].[Fax]
FROM [dbo].[Customers] AS [t0]
WHERE [t0].[City] = #p0
-- #p0: Input String (Size = 6; Prec = 0; Scale = 0) [London]
-- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 3.5.20810.0
AROUT
BSBEV
CONSH
EASTC
NORTS
SEVES
Alternately, you can use the LINQ to SQL Debug Visualizer to hover over a LINQ expression while in the VS 2008 debugger, and then inspect the raw SQL that the ORM will execute at runtime when evaluating the LINQ query expression.
I have a combo box in Silverlight. It has a collection of values built out of the properties of one of my LINQ-to-SQL objects (ie Name, Address, Age, etc...). I would like to filter my results based off the value selected in a combo box.
Example: Say I want everyone with a last name "Smith". I'd select 'Last Name' from the drop down list and enter smith into a textbox control. Normally I would write a LINQ query similar to...
var query = from p in collection where p.LastName == textbox.Text select p;
Is it possible to decide the property dynamically, maybe using Reflection? Something like
var query = from p in collection where p.(DropDownValue) == textbox.Text select p;
Assuming:
public class Person
{
public string LastName { get; set; }
}
IQueryable<Person> collection;
your query:
var query =
from p in collection
where p.LastName == textBox.Text
select p;
means the same as:
var query = collection.Where(p => p.LastName == textBox.Text);
which the compiler translates from an extension method to:
var query = Queryable.Where(collection, p => p.LastName == textBox.Text);
The second parameter of Queryable.Where is an Expression<Func<Person, bool>>. The compiler understands the Expression<> type and generates code to build an expression tree representing the lambda:
using System.Linq.Expressions;
var query = Queryable.Where(
collection,
Expression.Lambda<Func<Person, bool>>(
Expression.Equal(
Expression.MakeMemberAccess(
Expression.Parameter(typeof(Person), "p"),
typeof(Person).GetProperty("LastName")),
Expression.MakeMemberAccess(
Expression.Constant(textBox),
typeof(TextBox).GetProperty("Text"))),
Expression.Parameter(typeof(Person), "p"));
That is what the query syntax means.
You are free to call these methods yourself. To change the compared property, replace this:
typeof(Person).GetProperty("LastName")
with:
typeof(Person).GetProperty(dropDown.SelectedValue);
Scott Guthrie has a short series on dyamically built LINQ to SQL queries:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
That's the easy way...then there's another way that's a bit more involved:
http://www.albahari.com/nutshell/predicatebuilder.aspx
You can also use the library I created: http://tomasp.net/blog/dynamic-linq-queries.aspx. You would store the properties in ComboBox as lambda expressions and then just write:
var f = (Expression<Func<Product, string>>)comboBox.SelectedValue;
var query =
from p in collection
where f.Expand(textBox.Text)
select p;