I have a dynamic Linq query like this. I need to convert the result set into an array. But I am not able to convert the IQueryable type to an Array. Any suggestion?
my code:-
var query = Data.AsEnumerable()
.AsQueryable()
.Select("new(it[\"Country\"] as Country)", "it")
.Take(10);
foreach (string str in query) // **getting error Unable to cast object of type 'DynamicClass1' to type 'System.String**
{
}
I fixed it using like this :- foreach(var str in query) .
But I have another issue now. I have added where condition to the query. Now i am getting error "No property or field 'Country' exists in type 'DataRow'".
following is my query
var query= Data.AsEnumerable().AsQueryable().Where("Country = #0", "London").Select("new (Country as Country)");
When you use Dynamic LINQ all extensions returns collection with dynamic elements, so you need change your code for example like this
foreach (dynamic str in query)
{
....
}
also for your case str is object with field Country
UPDATE
for question from comment
if Data is DataTable when you call AsEnumerable or AsQueryable you work with collection of DataRow, so when you want filter it by column value you need use syntax for DataRow like this
Data.AsQueryable().Where("it[\"Country\"] = #0", "London")
or you can do select first like that
var query= Data.AsQueryable()
.Select("new (it[\"Country\"] as Country)")
.Where("Country = #0", "London")
UPDATE2
until you don't specify type for field it can be Object so you need change Select clause like this
....
.Select("new(Convert.ToString(it[\"Country\"]) as Country)")
....
in this case when you call Where after Select field Country will is String, so String have Contains method
Related
I have some errors using Linq on DataTable and I couldn't figure it out how to solve it. I have to admit that i am pretty new to Linq and I searched the forum and Internet and couldn't figure it out. hope you can help.
I have a DataTable called campaign with three columns: ID (int), Product (string), Channel (string). The DataTable is already filled with data. I am trying to select a subset of the campaign records which satisfied the conditions selected by the end user. For example, the user want to list only if the Product is either 'EWH' or 'HEC'. The selection criteria is dynaically determined by the end user.
I have the following C# code:
private void btnClick()
{
IEnumerable<DataRow> query =
from zz in campaign.AsEnumerable()
orderby zz.Field<string>("ID")
select zz;
string whereClause = "zz.Field<string>(\"Product\") in ('EWH','HEC')";
query = query.Where(whereClause);
DataTable sublist = query.CopyToDataTable<DataRow>();
}
But it gives me an error on line: query = query.Where(whereClause), saying
No property or field 'zz' exists in type 'DataRow'".
If I changed to:
string whereClause = "Product in ('EWH','HEC')"; it will say:
No property or field 'Product' exists in type 'DataRow'
Can anyone help me on how to solve this problem? I feel it could be a pretty simple syntax change, but I just don't know at this time.
First, this line has an error
orderby zz.Field<string>("ID")
because as you said, your ID column is of type int.
Second, you need to learn LINQ query syntax. Forget about strings, the same way you used from, orderby, select in the query, you can also use where and many other operators. Also you'll need to learn the equivalent LINQ constructs for SQL-ish things, like for instance IN (...) is mapped to Enumerable.Contains etc.
With all that being said, here is your query
var productFilter = new[] { "EWH", "HEC" };
var query =
from zz in campaign.AsEnumerable()
where productFilter.Contains(zz.Field<string>("Product"))
orderby zz.Field<int>("ID")
select zz;
Update As per your comment, if you want to make this dynamic, then you need to switch to lambda syntax. Multiple and criteria can be composed by chaining multiple Where clauses like this
List<string> productFilter = ...; // coming from outside
List<string> channelFilter = ...; // coming from outside
var query = campaign.AsEnumerable();
// Apply filters if needed
if (productFilter != null && productFilter.Count > 0)
query = query.Where(zz => productFilter.Contains(zz.Field<string>("Product")));
if (channelFilter != null && channelFilter.Count > 0)
query = query.Where(zz => channelFilter.Contains(zz.Field<string>("Channel")));
// Once finished with filtering, do the ordering
query = query.OrderBy(zz => zz.Field<int>("ID"));
I am using jqgrid in MVC 4. I have written a method for getting a list in linq.
In my function I am getting all values of jqgrid with search criteria i.e. Operator AND/OR
, operations Equals to, not equals to etc. Here I am also getting the column name like Name, City, State etc.
My problem is I can't pass the column name directly in linq query i.e. I have to use the column name as x => x.Name
switch (rule.field)
{
case "Name":
query = query.Where(x => x.Name.StartsWith(rule.data, StringComparison.OrdinalIgnoreCase));
break;
case "Course":
query = query.Where(x => x.Course.StartsWith(rule.data, StringComparison.OrdinalIgnoreCase));
break;
}
In rule.field I am getting column Name i.e. Name, city, state etc. I want to pass the column name which I am getting in rule.filed in LINQ query instead of x =>x.Name.
Is there any way to do it so I can avoid writing switch cases?
You can use System.Linq.Dynamic, which can be installed as a Nuget package along with string.Format. The syntax would then look something like..
var newquery = query.AsQueryable()
.Where(
string.Format("{0}.ToUpper().StartsWith(#0)", rule.field)
,rule.data.ToUpper());
You could always use reflection:
query = query.ToList().Where(p => {
var field = p.GetType().GetProperty(rule.field);
var value = (String) field.GetValue(p);
return value.StartsWith(rule.data, StringComparison.OrdinalIgnoreCase);
});
Warning: Reflection is slow. Only use this for short lists. Since you're dealing with UI rendering, I'm assuming this won't be a problem.
edit: My example is assuming all properties are indeed properties (and not fields), and that all properties are Strings. You may need to alter the code for your specific case.
I just performed a query with LINQ from the DAL and got a collection of a record with imbedded ILIST objects like the following
string name
date startDate
date endDate
ILIST<MyType> ImbeddedList (this contains more columns like recordID, sentDate, dueDate)
I need to return a LIST<T> back to the grid to be bounded.
I am having some problems with writing the LINQ statement to filter out the IQueryable collection object.
In my statement below:
IQueryable<All_DATA> cases = dalObject.GetData();
var mylist = cases.Select(s => {s.name, s.startDate, s.endDate,s.ImbeddedList????}).ToList();
When I get to the ImbeddedList, which is returned from the dalObject, the intellsense does not show the fields in the ImbeddedList. How can I correctly write the LINQ statement to filter for more fields in the ImbeddedList object?
As far I understand what you can do is
For fetching complete list from ImbeddedList
var mylist = cases.Select(s => {s.name, s.startDate, s.endDate, s.ImbeddedList}).ToList();
And for fetching individual field from ImbeddedList
var mylist = cases.SelectMany(s => s.ImbeddedList)
.Select(IItem => { IItem.Field1, IItem.Field2 }).ToList();
For more information please refer:
The Linq SelectMany Operator
LINQ - Get all items in a List within a List?
Using LINQ, select list of objects inside another list of objects
Use Google Search: "linq select list within list"
This is very confusing, I use AsDataView to bind query result to a dgv and it works fine with the following:
var query = from c in myDatabaseDataSet.Diamond where c.p_Id == p_Id select c;
dataGridView1.DataSource = query.AsDataView();
However, this one results in an Error:
var query = from item in myDatabaseDataSet.Items
where item.p_Id == p_Id
join diamond in myDatabaseDataSet.Diamond
on item.p_Id equals diamond.p_Id
join category in myDatabaseDataSet.DiamondCategory
on diamond.dc_Id equals category.dc_Id
select new
{
Product = item.p_Name,
Weight = diamond.d_Weight,
Category = category.dc_Name
};
dataGridView1.DataSource = query.AsDataView();
Error:
Instance argument: cannot convert from
'System.Collections.Generic.IEnumerable<AnonymousType#1>' to
'System.Data.DataTable'
AsDataView doesn't show up in query.(List). Why is this happen? How to bind the query above to the dgv then?.
The signature of the AsDataView is as follows:
public static DataView AsDataView(
this DataTable table
)
The only parameter is the DataTable.
The query you have is returning an IEnumerable of an anonymous type which doesn't have an implicit conversion to a DataTable (or a sequence of DataRow instances, in which case you could use that to help you create a DataTable).
You need to get the results back into a DataTable or something you can convert into a DataTable and then it will work.
In your particular case, it seems that you were (or are) using typed DataSets. If that is the case, then you should be able to take the values that were selected and then create new typed DataRow instances (there should be factory methods for you) which can then be put into a typed DataTable, which AsDataView can be called on.
just simply convert the result to a list and bind it to your grid.
var query = from item in myDatabaseDataSet.Items
where item.p_Id == p_Id
join diamond in myDatabaseDataSet.Diamond
on item.p_Id equals diamond.p_Id
join category in myDatabaseDataSet.DiamondCategory
on diamond.dc_Id equals category.dc_Id
select new
{
Product = item.p_Name,
Weight = diamond.d_Weight,
Category = category.dc_Name
}.ToList();
dataGridView1.DataSource = query;
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;