I want to create a bindingSource that supports sorting by multiple columns and attach it to a bindingNavigator.
I am using winforms and code-first EF.
I am constructing my query in the following manner
DbSet<Person> dset = DBContext.People;
string Searchstr ="Smith";
string sortby ="LastName, FirstName"
var qry = (IOrderedQueryable<Person>) dset.Where(
p => p.LastName.Contains(Searchstr) )
.OrderBy(sortby);
binding.datasource = dset.Local.ToBindingList(); // where binding has been dropped on form at design time.
binding.sort = sortby; // this is the line that screws up the sort order
I am using the extension method documented here to achieve the multi-column order by.
The problem turned out to be that I had set binding.sortby =sortby.
Using the multi column sortby was OK in the query because of the clever extension ( see link in the question) however it does not work to set the binding.sort to an expression involving multiple columns
The code works fine if I remove that line.
Related
I've the following Entity Model : Employee has a Company and a Company has Employees.
When using the Include statement like below:
var query = context.Employees.Include(e => e.Company);
query.Dump();
All related data is retrieved from the database correctly. (Using LEFT OUTER JOIN on Company table)
The problem is hat when I use the GroupBy() from System.Linq.Dynamic to group by Company.Name, the Employees are missing the Company data because the Include is lost.
Example:
var groupByQuery = query.GroupBy("new (Company.Name as CompanyName)", "it");
groupByQuery.Dump();
Is there a way to easily retrieve the applied Includes on the 'query' as a string collection, so that I can include them in the dynamic GroupBy like this:
var groupByQuery2 = query.GroupBy("new (Company, Company.Name as CompanyName)", "it");
groupByQuery2.Dump();
I thought about using the ToString() functionality to get the SQL Command like this:
string sql = query.ToString();
And then use RegEx to extract all LEFT OUTER JOINS, but probably there is a better solution ?
if you're creating the query in the first place - I'd always opt to save the includes (and add to them if you're making a composite query/filtering).
e.g. instead of returning just 'query' return new QueryContext {Query = query, Includes = ...}
I'd like to see a more elegant solution - but I think that's your best bet.
Otherwise you're looking at expression trees, visitors and all those nice things.
SQL parsing isn't that straight either - as queries are not always that simple (often a combo of things etc.).
e.g. there is a `span' inside the query object (if you traverse a bit) which seems to be holding the 'Includes' but it's not much help.
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 })
LINQ to Entities 3.5 doesn't support String.Join so I'm binding my gridview to a property I define outside the Select statement. Obviously it's not letting me sort on RecipientNames because it's just an IEnumerable and that doesn't make sense. How can I use LINQ to Entities to sort on my new column? If possible I'd like to get rid of RecipientNamesList altogether and create something that LINQ will be able to handle for sorting.
IQueryable<NotificationDetail> resultsFlattened = results.Select(n => new NotificationDetail()
{
..
RecipientNames = n.NotificationRecipients.Select(nr => nr.Recipient.RecipientNameFirst + " " + nr.Recipient.RecipientNameLast).Where(s => s.Trim().Length > 0)});
});
IQueryable<NotificationDetail> resultsPaged = ApplySortingPaging(resultsFlattened,SortPageOptions);
return resultsPaged.ToEntityList(results.Count()); //blows up here, obviously
public string RecipientNamesList
{
get
{
return String.Join(", ", RecipientNames.ToArray());
}
}
It blows up because the sort cannot be translated into SQL. The easy solution is to make sure you perform the sort locally and not in SQL Server. Just add a ToList or AsEnumerable after the first query.
resultsFlattened = resultsFlattened.ToList();
You'll want to ensure that you do your paging before this, otherwise you could be pulling down a large number of rows from the database.
Or you use the Linq.Translations library developed by by Damien Guard and others. It enables you to use local, calculated properties just as you require.
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.
DynamicObject LINQ query with the List compiles fine:
List<string> list = new List<string>();
var query = (from dynamic d in list where d.FirstName == "John" select d);
With our own custom class that we use for the "usual" LINQ compiler reports the error "An expression tree may not contain a dynamic
operation":
DBclass db = new DBclass();
var query = (from dynamic d in db where d.FirstName == "John" select d);
What shall we add to handle DynamicObject LINQ?
Does DBClass implement IEnumerable? Perhaps there is a method on it you should be calling to return an IEnumerable collection?
You could add a type, against which to write the query.
I believe your problem is, that in the first expression, where you are using the List<>, everything is done in memory using IEnumerable & Link-to-Objects.
Apparently, your DBClass is an IQueryable using Linq-to-SQL. IQueryables use an expression tree to build an SQL statement to send to the database.
In other words, despite looking much alike, the two statements are doing radically different things, one of which is allowed & one which isn't. (Much in the way var y = x * 5; will either succeed or fail depending on if x is an int or a string).
Further, your first example may compile, but as far as I can tell, it will fail when you run it. That's not a particular good benchmark for success.
The only way I see this working is if the query using dynamic is made on IEnumerables using Link-to-Objects. (Load the full table into a List, and then query on the list)