foreach (ReportType t in reportsCollection)
{
List<Report> reps = (from r in t.reports where r.isChecked == true select r).ToList<Report>();
foreach (Report r in reps)
System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo(r.path));
}
This statement works just fine. I'm just looking for a single LINQ statement that could maybe do this.
Basically, I have a report object with a property called isChecked. reportsCollection contains several reportTypes that contains lists of reports of that type. So the collection looks like this:
type1
report
report 2
report 3
type 2
report 4
report 5
report 6
and so on.
I want a LINQ statement that will grab all reports where isChecked == true within those types. I suspect a loop is necessary, but I was curious to see if the community had a solution. Thanks!
You want to use SelectMany
var query = reportsCollection.SelectMany(t => t.reports)
.Where(r => r.isChecked == true)
.ToList();
In query expression syntax form, you might write it as
var query = (from type in reportsCollection
from report in type.reports
where report.isChecked == true
select report).ToList();
In query syntax it will look like this
var query = from t in reportCollection
from r in t.reports
where r.isChecked == true
select r;
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 want to get the latest record of each group from a SQL Server table using Linq.
Table Example:
I want to get this result:
My Linq query returns one record for each company, but it doesn't return the most recent ones:
var query = from p in db.Payments
where p.Status == false
&& DateTime.Compare(DateTime.Now, p.NextPaymentDate.Value) == 1
group p by p.CompanyID into op
select op.OrderByDescending(nd => nd.NextPaymentDate.Value).FirstOrDefault();
What am i missing here? Why isn't the NextPaymentDate being ordered correctly?
!!UPDATE!!
My query is working as expected. After analysing #Gilang and #JonSkeet comments i ran further tests and found that i wasn't getting the intended results due to a column that wasn't being updated.
var query = from p in db.Payments
where p.Status == false
group p by p.CompanyID into op
select new {
CompanyID = op.Key,
NextPaymentDate = op.Max(x => x.NextPaymentDate),
Status = false
};
The reason your query is not being ordered correctly is that your query does not do proper grouping. You did correctly grouping by CompanyID, but then you have to retrieve the maximum NextPaymentDate by calling aggregate function.
Status can be assigned false because it is already filtered by Where clause in the early clauses.
I have a linq query which I want to add some additional, optional WHERE conditions to using LinqKit Predicate Builder. However, I an struggling to get the additional predicate to work
This is my initial query:
var query = (from OP in ctx.OrganisationProducts
where OP.OrganisationID == orgID
orderby OP.Product.Name, OP.Product.VersionName
select OP).Include("Product");
As you can see, there is JOIN in there.
I then wish to add additional predicates if required:
if(!includeDisabledP42Admin || !includeDisabledOrgAdmin)
{
var pred = PredicateBuilder.True<OrganisationProduct>();
if (!includeDisabledP42Admin)
pred.And(op => op.Enabled);
if (!includeDisabledOrgAdmin)
pred.And(op => op.AccessLevel == "NA" || op.AccessLevel == "NU");
query = query.Where(pred);
}
However, the generated SQL is unchanged and the query returns the same number of rows.
I thought I might have had to do the Expand conversion as so:
query = query.AsExpandable().Where(pred);
But this causes a runtime error.
I think the issue is the fact that I am adding the predicate to a query that is already no longer a pure OrganisationProduct object, however I would like advise on how I insert my predicate at the right place.
Thanks and all :-)
You have to assign the return value of And to the predicate:
pred = pred.And(op => op.Enabled);
Side note: you may like this predicate builder that works without Expand/AsExpandable, but has the same syntax.
I have a collection of NHibernate objects ConcurrentBag<Event> with properties project_id and name. I want to a set of unrelated (schema wise) objects from another table which also match these properties.
The SQL I would expect would look something like:
SELECT * FROM table WHERE (project_id = 1 AND name = 'foo')
OR (project_id = 2 AND name = 'foo')
OR (project_id = 1 AND name = 'bar')
... etc
The pairs of values in the WHERE clause are based on the values from each Event in the ConcurrentBag<Event>.
I am not sure how to query this with NHibernate (ideally with LINQ). Is this even possible?
This would be difficult with LINQ I think, but if you use QueryOver it's easy to build a WHERE clause dynamically using Restrictions.Disjunction:
var disjunction = Restrictions.Disjunction();
foreach (Event evt in events)
{
disjunction.Add(Restrictions.Where<Table>(
t => t.project_id == evt.project_id && t.name == evt.name);
}
var rows = session.QueryOver<Table>()
.Where(disjunction)
.List<Table>();
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;