I am just getting started with Linq, WPF and Silverlight. I am trying to display data which originates from a XML document in a DataGrid. I use a Linq query to select the objects I want and link the result to the DataGrid.
XDocument doc = GedView.GedcomConverter.ConvertToXml(new StreamReader(e.Result));
var query = from person in doc.Descendants("INDI")
select new PersonInfo()
{
Id = (string)person.Attribute("Value"),
GedcomName = (string)person.Descendants("NAME").SingleOrDefault().Attribute("Value"),
Sex = (string)person.Descendants("SEX").SingleOrDefault().Attribute("Value"),
BirthDate = GedcomConverter.ConvertDate(person.Descendants("BIRT").SingleOrDefault()),
DeathDate = GedcomConverter.ConvertDate(person.Descendants("DEAT").SingleOrDefault()),
BurialDate = GedcomConverter.ConvertDate(person.Descendants("BURI").SingleOrDefault()),
};
DataGrid.ItemsSource = query;
DataGrid.SelectedIndex = -1;
However, when the grid is scrolled, the performance is bad. I notice that the ConvertDate method is called many times. (The ConvertDate method converts a human-readable date string into a DateTime? object.)
Why is this? I had assumed that the 'query' would be executed once and not continuously.
What would be the right way to do this? I am using a query because I will want to add some kind of filter to restrict the items in the list at a later date.
Thanks
Try:-
DataGrid.ItemsSource = query.ToList();
The DataGrid is not expecting the IEnumerable that it is accessing to cause something very expensive to happen when it gets an enumerator to find items. However by passing the query itself to the DataGrid you cause the query to execute every time data grid calls GetEnumerator.
Since you want to filter at a later date you could simply re-assign the ItemsSource when you change your filter settings.
Related
Here is my scenario. I have a Document class. The document is associated with a DocumentClasses table through a many to many relationship, so a document can have one or more classes. When running a search, the user can choose to filter documents by class. So, I need to be able to append a where clause to my query if the user chooses to select any classes. The logic is that if the document is assigned to any of the classes in the classes the user selected, the document should be returned. So the basic query needed in pseudo code. So basically, if any number in list A belongs to list B, then return the record.
I have tried this (RestrictByClasses is just a List(Of Integer)):
query = query.where(Function(resultItem) RestrictByClasses.Contains(resultItem.DocumentClassIds.Any())
But I get the following exception:
The nested query is not supported. Operation1='Case' Operation2='Collect'
Is there any way to get linq to filter records out like this?
Thanks!
UPDATE:
After doing a little more debugging, I think that it is more to do with how I am projecting onto the object in order to load it with values that can be used to filter. Here is how I am doing the projection:
Dim query = From document In dbContext.Documents
Select New FeeAndReceptionReportIntermediateItem With
{
.BookTypeId = If(restrictByBookTypes AndAlso document.DocumentInstruments.Any(), document.DocumentInstruments.FirstOrDefault().Instrument.BookTypeId, Nothing),
.CustomerId = document.CustomerId,
.DocumentClassIds = If(restrictByDocumentClasses, document.DocumentClasses.Select(Function(group) group.ClassId), Nothing),
.DocumentId = document.DocumentId,
.DocumentNumber = document.DocumentNumber,
.DepartmentId = document.DepartmentId,
.InstrumentGroupIds = If(restrictByInstrumentGroup, document.DocumentInstruments.FirstOrDefault().Instrument.InstrumentGroups.Select(Function(group) group.InstrumentGroupId), Nothing),
.RecordDateTime = document.RecordDateTime,
.RestrictedInstrument = (includeRestrictedDocuments AndAlso document.DocumentInstruments.Any() AndAlso document.DocumentInstruments.FirstOrDefault().Instrument.Restricted)
}
I think it is complaining about how the .DocumentClassIds and .InstrumentGroupId's are being loaded into the POCO object (FeeAndReceptionReportIntermediateItem). I would really like to load these up in the initial query, before a .ToList() has been called and I would really like to not even do the join if the user did not pass in the restrictions that require me to create the join, that's why I am using the navigation properties and an if statement when loading these collecctions, because I am assuming if "restrictByDocumentClasses" is false, the navigation property won't be accessed and the join won't be included.
This works as a general pattern. The first line gets an IQueryable<> from the DbSet<>. The select does this for us, so that we can continue reusing query to hold our query as we build it up. Then just keep adding on If...Then...query=query.Where(...)...Endif to continue whittling down the resultset.
var query=db.MyTable.Select(x=>x);
if (RestrictByClasses.Any())
query=query.Where(r =>
r.DocumentClasses.Select(x=>x.ClassId)
.Intersect(RestrictByClasses)
.Any());
if (RestrictBySomethingElse)
query=query.Where(x=>SomethingElse)
I think this is the equivalent in VB.NET:
Dim query = db.MyTable.[Select](Function(x) x)
If RestrictByClasses.Any() Then
query = query.Where(Function(r) r.DocumentClasses.Select(Function(group) group.ClassId).Intersect(RestrictByClasses).Any())
End If
'Repeat as necessary
If RestrictBySomethingElse Then
query = query.Where(Function(x) SomethingElse)
End If
'End repeat
' Rest here is pseudo code
' Sort
SELECT/SWITCH sortonfield
CASE 'name': query=query.OrderBy(Function(x) x.name)
CASE 'dob': query=query.OrderBy(Function(x) x.dob)
DEFAULT: query=query.OrderBy(Function(x) x.id)
END CASE
'Paginate
query=query.Skip((pagenumber-1)*pagesize).Take(pagesize)
'Project
Dim finalresult=query.Select(Function(x) new something {
name=x.Name,
id=x.id,
things=x.things
});
Once all your filters have been put in place (and optionally a sort, and pagination), then project your resultset into whatever you need.
I am trying to bind distinct records to a dropdownlist. After I added distinct function of the linq query, it said "DataBinding: 'System.String' does not contain a property with the name 'Source'. " I can guarantee that that column name is 'Source'. Is that name lost when doing distinct search?
My backend code:
public IQueryable<string> GetAllSource()
{
PromotionDataContext dc = new PromotionDataContext(_connString);
var query = (from p in dc.Promotions
select p.Source).Distinct();
return query;
}
Frontend code:
PromotionDAL dal = new PromotionDAL();
ddl_Source.DataSource = dal.GetAllSource();
ddl_Source.DataTextField = "Source";
ddl_Source.DataValueField = "Source";
ddl_Source.DataBind();
Any one has a solution? Thank you in advance.
You're already selecting Source in the LINQ query, which is how the result is an IQueryable<string>. You're then also specifying Source as the property to find in each string in the databinding. Just take out the statements changing the DataTextField and DataValueField properties in databinding.
Alterantively you could remove the projection to p.Source from your query and return an IQueryable<Promotion> - but then you would get distinct promotions rather than distinct sources.
One other quick note - using query syntax isn't really helping you in your GetAllSources query. I'd just write this as:
public IQueryable<string> GetAllSource()
{
PromotionDataContext dc = new PromotionDataContext(_connString);
return dc.Promotions
.Select(p => p.Source)
.Distinct();
}
Query expressions are great for complicated queries, but when you've just got a single select or a where clause and a trivial projection, using the dot notation is simpler IMO.
You're trying to bind strings, not Promotion objects... and strings do not have Source property/field
Your method returns a set of strings, not a set of objects with properties.
If you really want to bind to a property name, you need a set of objects with properties (eg, by writing select new { Source = Source })
I am using Northwind Customers Table where I fill the dataset and get the datatable.
I am trying to use dynamic linq and want to select columnName dynamically
var qry = MyDataTable.AsEnumerable().AsQueryable().Select("new(Country)");
Right now I have hard coded country but even then I get this error
No property or field 'Country' exists in type 'datarow'
I would like to eventually change this query to take the column name dynamically.
Please help!!! thanks.
The important hint is here (in bold):
No property or field 'Country' exists
in type 'datarow'
The extension method AsEnumerable of the DataTable class returns an IEnumerable<T> where T has the type DataRow. Now the Select method of Dynamic LINQ wants to work with this type DataRow which hasn't a property Country of course.
You could try this instead:
var qry = MyDataTable.AsEnumerable().AsQueryable()
.Select("new(it[\"Country\"] as CountryAlias)");
it now represents a variable of type DataRow and you can use methods of this type and perhaps also the indexer in my example above. (Dynamic LINQ supports accessing array elements by an integer index, but I am not sure though if accessing an indexer with a string key will work.)
I've used Slauma's answer and it worked. In addition i was doing OrderBy with dynamic linq maybe this will help to someone. I'll just drop the code here.
string dynamicLinqText = $"it[\"{sortColumnName}\"] {sortDirection}"; //it["PERSON_NAME"] asc
result = result.AsEnumerable().OrderBy(dynamicLinqText).CopyToDataTable();
I have a Typed DataSet DataTable which inherits TypedTableBase<T>, which in turn implements IEnumerable<T>. I can't seem to get this to work.
myDataTable.OrderBy(x => x.ID).ThenBy(y => y.ID2);
Instead I have to assign this statement to an IEnumerable(or List), then refill my DataTable manually with the newly ordered IEnumerable before I commit. Is this how it is intended to be? I've thought about creating my own extension method that will empty/refill my DataTables, but would this be wise?
Note: Typically I only need to sort for viewing purposes using DataView. But in this case I have a custom routine that must create a new access database with sorting requirements, which means I need to sort the actual DataTable so that I may re-commit it.
Thank you.
In order to do what you want, you must add the following reference to your project:
System.Data.DataSetExtensions
Once you have that added, you can order your DataTable like this:
var query = myDataTable.OrderBy(x => x.ID).ThenBy(y => y.ID2);
// use the DataView generated from the LINQ query
DataView dtv = query.AsDataView();
In order to iterate through the DataView, you can do the following:
var dtv = query.AsDataView();
foreach(DataRowView rw in dtv)
{
// you can also cast back to the typed data...
MyCustomRowType typedRow = (MyCustomRowType) rw.Row;
// do something here...
}
Alternatively you can typecast via LINQ this way:
var dtv = query.AsDataView().Cast<MyCustomRowType>();
// rowItem is of type MyCustomRowType...
foreach(var rowItem in dtv)
{
// do something here...
}
Linq extension methods do not alter the source enumerable.
var numbers = new int[]{1,2,3};
var reversed = numbers.OrderByDescending(x=>x);
foreach(var number in reversed)
Console.Write(number); // 321
foreach(var number in numbers)
Console.Write(number); // 123
If you want to sort a DataTable, you should be using DataViews. You create a view on your DataTable, then apply a Sort or Filter to it, then bind against it. Keep in mind DataSets are an older technology and not quite up to date on the latest and the greatest. A "newer" approach would be to use the Entity Framework.
Ok this should be really simple, but I am doing my head in here and have read all the articles on this and tried a variety of things, but no luck.
I have 3 tables in a classic many-to-many setup.
ITEMS
ItemID
Description
ITEMFEATURES
ItemID
FeatureID
FEATURES
FeatureID
Description
Now I have a search interface where you can select any number of Features (checkboxes).
I get them all nicely as an int[] called SearchFeatures.
I simply want to find the Items which have the Features that are contained in the SearchFeatures.
E.g. something like:
return db.Items.Where(x => SearchFeatures.Contains(x.ItemFeatures.AllFeatures().FeatureID))
Inside my Items partial class I have added a custom method Features() which simply returns all Features for that Item, but I still can't seem to integrate that in any usable way into the main LINQ query.
Grr, it's gotta be simple, such a 1 second task in SQL. Many thanks.
The following query will return the list of items based on the list of searchFeatures:
from itemFeature in db.ItemFeatures
where searchFeatures.Contains(itemFeature.FeatureID)
select itemFeature.Item;
The trick here is to start with the ItemFeatures table.
It is possible to search items that have ALL features, as you asked in the comments. The trick here is to dynamically build up the query. See here:
var itemFeatures = db.ItemFeatures;
foreach (var temp in searchFeatures)
{
// You will need this extra variable. This is C# magic ;-).
var searchFeature = temp;
// Wrap the collection with a filter
itemFeatures =
from itemFeature in itemFeatures
where itemFeature.FeatureID == searchFeature
select itemFeature;
}
var items =
from itemFeature in itemFeatures
select itemFeature.Item;