I have C# code to populate a dropdown list in Silverlight which works fine except when there are duplicates. I think because IEnumerable<Insurance.Claims> is a collection, it filters out duplicates. How would I code my LINQ query to accept duplicates?
My Sample Data looks like:
Code => CodeName
FGI Field General Initiative
SRI Static Resource Initiative
JFI Joint Field Initiative - This is "overwritten" in results
JFI Joint Friend Initiative
IEnumerable<Insurance.Claims> results;
// ADO.NET Data Service
var claim = (from c in DataEntities.Claims.Expand("Claimants").Expand("Policies")
where c.Claim_Number == claimNumber
select c);
DataServiceQuery<Insurance.Claims> dataServiceQuery =
claim as DataServiceQuery<Insurance.Claims>;
dataServiceQuery.BeginExecute((asyncResult) =>
{
results = dataServiceQuery.EndExecute(asyncResult);
if (results == null)
{
// Error
}
else
{
// Code to populate Silverlight form
}
});
(Not sure if you're still struggling with this but anyway...)
I'm pretty sure it's not the IEnumerable interface but the actual drop down that is causing this behaviour. The code is being used as the key, and so obviously each time the same code is encountered, the item is being overwritten.
I don't think you can override this unless you change the code, or use another identifier as the key field in the dropdown.
You may want to add a try-catch block around dataServiceQuery.EndExecute(asyncResult) to properly handle errors.
Related
I'm using EF Core but I'm not really an expert with it, especially when it comes to details like querying tables in a performant manner...
So what I try to do is simply get the max-value of one column from a table with filtered data.
What I have so far is this:
protected override void ReadExistingDBEntry()
{
using Model.ResultContext db = new();
// Filter Tabledata to the Rows relevant to us. the whole Table may contain 0 rows or millions of them
IQueryable<Measurement> dbMeasuringsExisting = db.Measurements
.Where(meas => meas.MeasuringInstanceGuid == Globals.MeasProgInstance.Guid
&& meas.MachineId == DBMatchingItem.Id);
if (dbMeasuringsExisting.Any())
{
// the max value we're interested in. Still dbMeasuringsExisting could contain millions of rows
iMaxMessID = dbMeasuringsExisting.Max(meas => meas.MessID);
}
}
The equivalent SQL to what I want would be something like this.
select max(MessID)
from Measurement
where MeasuringInstanceGuid = Globals.MeasProgInstance.Guid
and MachineId = DBMatchingItem.Id;
While the above code works (it returns the correct value), I think it has a performance issue when the database table is getting larger, because the max filtering is done at the client-side after all rows are transferred, or am I wrong here?
How to do it better? I want the database server to filter my data. Of course I don't want any SQL script ;-)
This can be addressed by typing the return as nullable so that you do not get a returned error and then applying a default value for the int. Alternatively, you can just assign it to a nullable int. Note, the assumption here of an integer return type of the ID. The same principal would apply to a Guid as well.
int MaxMessID = dbMeasuringsExisting.Max(p => (int?)p.MessID) ?? 0;
There is no need for the Any() statement as that causes an additional trip to the database which is not desirable in this case.
I have the following LINQ to Entities call to fill a collection variable:
var insuredFamily = db.Insureds.Where(x => x.ssn.Split('-')[0] == tmp[MemberId])
.OrderBy(x => x.fk_relation);
How would I go about looping through the items in the collection printing out both the item header and the item value for each row?
I'm new to LINQ to Entities, so all I'm trying to do is loop through a built collection and output the headers and rows to a log file so that I can quickly see what is being returned in the collection without resorting to stepping through each row in the debugger. Is this possible?
If a generic loop is not possible, is it possible to set the data source of a data grid to the collection variable and view the collection in a grid?
For starters, this can't be a LINQ-to_Entities statement. There's no way to translate x.ssn.Split('-')[0] == tmp[MemberId] into SQL. Unless this is EF-Core, that automatically switches to client-side evaluation when the expression contain not-supported part. You're not explicit about that.
Anyway, it's overkill to add logging just to see the content of a collection while debugging. You can use the immediate window in Visual Studio to output data when the code stops at a break point.
To make this really helpful, override the Insured class's ToString method. When I do this with just some Product class ...
public override string ToString()
{
return string.Format("{0}, {1}", this.Name, this.UnitPrice);
}
... and break in the debugger right after a line like ...
var prod = context.Products;
.. then in the immediate window I can type ...
?prod.ToList()
... which gives me:
Count = 6
[0]: {Nike Air, 150.00}
[1]: {Web cam, 23.00}
[2]: {Mouse, 7.00}
[3]: {Cool pack, 4.50}
[4]: {Keyboard, 47.30}
[5]: {Action cam, 73.00}
(and some SQL logging)
Note that this is invasive debugging. By calling ToList, the query is forced to execute. This may change the state in a way that it affects the code's behavior. The same would hold for logging though.
Thank you for all the advice, but it looks like the following two lines of code will do what I need. I just wanted to visualize the results of my LINQ to SQL queries.
var nationalities = db.Nationalities.OrderBy(x => x.pk_Nationality);
dgvResults.DataSource = nationalities;
This code will simply put the collection into the data source of my data grid view allowing me to see all the contents.
I am using LinqPad to test my query. This query works when the LInqPad connection is to my database (LInq to SQL) but it does not work when I change the connection to use my Entity Framework 5 Model.dll. (Linq to Entity). This is in C#.
I have two tables called Plan and PlanDetails. Relationship is one Plan to many PlanDetails.
var q = from pd in PlanDetails
select new {
pd.PlanDetailID,
ThePlanName = (from p in this.Plans
where p.PlanID == pd.PlanID
select p.PlanName)
};
var results = q.ToList();
q.Dump(); //This is a linqpad method to output the result.
I get this error "NotSupportedException: Unable to create a constant value of type 'Domain.Data.Plan'. Only primitive types or enumeration types are supported in this context." Any ideas why this only works with Linq to SQL?
basically it means you are using some complex datatype inside the query for comparison.
in your case i suspect from p in this.Plans where p.PlanID == pd.PlanID is the culprit.
And it depends on DataProvider. It might work for Sql Data Provider, but not for SqlCE data Provider and so on.
what you should do is to convert your this.Plans collection into a primitive type collection containing only the Ids i.e.
var integers = PlanDetails.Plans.Select(s=>s.Id).ToList();
and then use this list inside.
var q = from pd in PlanDetails
select new {
pd.PlanDetailID,
ThePlanName = (from p in integers
where p == pd.PlanID
select pd.PlanName)
};
I got this error when i was trying to null check for a navigational property in the entity framework expression
I resolved it by not using the not null check in the expression and just using Any() function only.
protected Expression<Func<Entities.Employee, bool>> BriefShouldAppearInSearchResults(
IQueryable<Entities.Employee> briefs, string username)
{
var trimmedUsername = NameHelper.GetFormattedName(username);
Expression<Func<Entities.Employee, bool>> filterExpression = cse =>
cse.Employee.Cars.All(c =>
c.Employee.Cars!=null && <--Removing this line resolved my issue
c.Employee.Cars.Any(cur => cur.CarMake =="Benz")));
return filterExpression;
}
Hope this helps someone!
This is a Linqpad bug if you like (or a peculiarity). I found similar behaviour myself. Like me, you may find that your query works with an ObjectContext, but not a DbContext. (And it works in Visual Studio).
I think it has to do with Linqpad's inner structure. It adds MergeAs (AppendOnly) to collections and the context is a UserQuery, which probably contains some code that causes this bug.
This is confirmed by the fact that the code does work when you create a new context instance in the Linqpad code and run the query against this instance.
If the relationship already exists.
Why not simply say.
var q = from pd in PlanDetails
select new {
pd.PlanDetailID,
ThePlanName = pd.Plan.PlanName
};
Of course i'm assuming that every PlanDetail will belong to a Plan.
Update
To get better results from LinqPad you could tell it to use your own assembly (which contains your DbContext) instead of the default Datacontext it uses.
I'm wondering about the best usage of the delete method in nhibernate.
If you go the entity than just call delete and send it, but if not you need to query it or write a query and send it to delete method.
I'm wondering if its possible to write a linq expression and send it to delete.
Is it possible to perform a Linq transformation to hql and than call session.Delete(query)
with the generated hql?
I want to call Session.Delete, and give it a linq so it can know what to delete without selecting the data. Do you know a class that can convert linq expression to hql?
You now can directly in linq with NHibernate 5.0
//
// Summary:
// Delete all entities selected by the specified query. The delete operation is
// performed in the database without reading the entities out of it.
//
// Parameters:
// source:
// The query matching the entities to delete.
//
// Type parameters:
// TSource:
// The type of the elements of source.
//
// Returns:
// The number of deleted entities.
public static int Delete<TSource>(this IQueryable<TSource> source);
Exemple:
var tooOldDate = System.DateTime.Now.AddYears(5);
session.Query<User>()
.Where(u => u.LastConnection <= tooOldDate)
.Delete();
The Q in LINQ stands for "Query". So, no, you can't use a LINQ expression for delete.
That said, NH's query language, HQL, does support that.
In the same way that you can say "from Foo where Bar = :something" to get all the foos matching a condition, you can do this:
session.CreateQuery("delete Foo where Bar = :something")
.SetParameter("something", ...)
.ExecuteUpdate();
I have submitted a pull request for NH-3659 - Strongly Typed Delete. The link is available at nhibernate.jira.com/browse/NH-3659.
I know this is an old question but for those reading this now. NHibernate 5 released Oct 10, 2017 has added a Delete Linq extension
from documentation 17.6.3. Deleting entities
Delete method extension expects a queryable defining the entities to delete. It immediately deletes them.
session.Query<Cat>()
.Where(c => c.BodyWeight > 20)
.Delete();
I'm sure it would be possible to do what you want but the bottom line is that it doesn't make a lot of sense (not sure why you want to give NHibernate the select criteria when you can do it in a single statement, your approach would end up causing 2 hits to the database), having said that, one easy option you could do, is query the IDs using LINQ and pass those to NHibernate
int[] deleteIds = (from c in Customer where {some condition} select c.Id).ToArray<int>();
session.CreateQuery("delete Customer c where c.id in (:deleteIds)")
.SetParameterList("deleteIds", deleteIds)
.ExecuteUpdate();
I want to do something like
from table1
where col5="abcd"
select col1
I did like
query_ = From g In DomainService.GetGEsQuery Select New GE With {.Desc = g.codDesc}
"This cause a runtime error, i tried various combinations but failed"
please help.
I'm assuming your trying to do this on the client side. If so you could do something like this
DomainService.Load(DomainService.GetGEsQuery().Where(g => g.codDesc == "something"), lo =>
{
if (lo.HasError == false)
{
List<string> temp = lo.Entities.Select(a => a.Name).ToList();
}
}, null);
you could also do this in the server side (which i would personally prefer) like this
public IQueryable<string> GetGEStringList(string something)
{
return this.ObjectContext.GE.Where(g => g.codDesc == something).Select(a => a.Name);
}
Hope this helps
DomainService.GetGEsQuery() returns an IQueryable, that is only useful in a subsequent asynchronous load. Your are missing the () on the method call, but that is only the first problem.
You can apply filter operations to the query returned using Where etc, but it still needs to be passed to the Load method of your domain context (called DomainService in your example).
The example Jack7 has posted shows an anonymous callback from the load method which then accesses the results inside the load object lo and extracts just the required field with another query. Note that you can filter the query in RIA services, but not change the basic return type (i.e. you cannot filter out unwanted columns on the client-side).
Jack7's second suggestion to implement a specific method server-side, returning just the data you want, is your best option.