Please bear with me I'm not to hot on LINQ and even less on C# but I have the following statement that's causing me a headache:
myList = myClass.Where(f => f.OrigiFilename == origiFilename).ToList();
It works okay currently but needs changing.
I understand the where clause returns a result set of filenames and we are going to compare them to the variable
origiFilename
So we essence we are comparing like so: file1.txt == file1, file2.doc == file1, file3.pdf == file1
However, what must happen is we want to ignore the file extension that is returned from
f.OrigiFilename
I'd ideally want to use Get File Name Without Extension but I can't seem to do this in LINQ or be able to switch to C# to do this and then back.
Any LINQ experts out there ever have to do this?
I do have a workaround which is add the lot into the list and then move though the list again removing each using C# but this isn't ideal, I want it all done in one statement...
Do you mean this?
myClass
.Where(f => Path.GetFileNameWithoutExtension(f.OrigiFilename) == origiFilename)
.ToList();
Unfortunately, if you want to keep the query on the database side, there isn't an easy way to jump back to C#, however, you can do the following, which should translate into decent SQL query, albeit there are some differences and will fail if there are multiple extensions on the filename:
myList = myClass.Where(f => f.OrigiFilename.StartsWith(origiFilename+".")).ToList();
The Path class contains a GetFileNameWithoutExtension() method that you can use:
myList = myClass
.Where(f => Path.GetFileNameWithoutExtension(f.OrigiFilename) == origiFilename)
.ToList();
Related
Here is what my model looks like:
I'm trying to get the count of distinct Assesors by a certain EventId.
Here's the code I'm trying to use:
var x = db.Assessors.Select(a => (a.Assessments.Select(y => y.EventFacility.EventId == 138))).Count();
Unfortunately, I must be coding this wrong because instead of getting the expected result (a count of 9, in this case) I'm getting the wrong result: 35.
I'm wondering if someone can take a look at my LINQ statement and tell me what I'm doing wrong?
You need to use Where and Any like this:
var result = db.Assessors
.Where(a => a.Assessments.Any(y => y.EventFacility.EventId == 138));
What this is saying is that you want all Assessors that are parents of any Assessment that is related to that particular Event.
You're going about this backward, start from what you know (the event since you have it's ID) and navigate to what you want through the navigation properties.
It's impossible to tell from your schema as it includes neither the properties nor the mapping type 1:1? 1:N? Can't know from simple lines
It would probably look Something like this
var x = db.Events
.Where(ev=>ev.Id == 138)
.SelectMany(ev=>ev.EventFacilities) //(i'm assumine possibly multiple and not 1 per event, once again schema doesn't show it, if it's not the case change SelectMany to Select)
.SelectMany(ef=>ef.Assesments) // Same assumption as above
.Select(as=>as.Assessor) // Asuming otherwise here, if wrong change Select to SelectMany
.Distinct(); // Ignore duplicate assessors
Note that your question is impossible to answer as is, this is a best effort but if you want help you should give "all" the information required, not strip out what doesn't immediately seem relevant, it would've been much easier if you took an actual screenshot of your entity diagram instead of what you made up.
Is that possible in LINQ to write a nice one-liner to get a first matched element or if there's no match than get first element in the collection?
E.g. you have a collection of parrots and you want yellow parrot but if there's no yellow parrots - then any will do, something like this:
Parrots.MatchedOrFirst(x => x.Yellow == true)
I'm trying to avoid double-go to SQL Server and the ORM we use in this particular case is Dapper.
What about:
var matchedOrFirst = Parrots.FirstOrDefault(x => x.Yellow == true)
?? Parrots.FirstOrDefault();
Edit
For structs, this should work:
var matchedOrFirst = Parrots.Any(x => x.Yellow == true)
? Parrots.First(x => x.Yellow == true)
: Parrots.FirstOrDefault();
Edit: It was a linq to SQL solution
First building a handy extension
public static T MatchedOrFirstOrDefault<T>(this IQueryable<T> collection, System.Linq.Expressions.Expression<Func<T, Boolean>> predicate)
{
return (from item in collection.Where(predicate) select item)
.Concat((from item in collection select item).Take(1))
.ToList() // Convert to query result
.FirstOrDefault();
}
Using the code
var matchedOrFirst = Parrots.MatchedOrFirstOrDefault(x => x.Yellow);
If you want to avoid a 2nd SQL call and since requires branching logic, its unlikely that Dapper will know how to convert a LINQ query you come up with into appropriate SQL IIF, CASE, or whatever other SQL-specific functions you end up using.
I recommend you write a simple stored procedure to do that and call it from Dapper.
Depending on its usage though, if this page only has one or two queries on it already, and is located reasonably close (latency wise) to the server, a 2nd simple SELECT won't hurt the overall application that much. Unless it is in a loop or something, or your example is trivial compared to the actual query regarding the cost of the first SELECT.
I'm using LINQ to search multiple fields on a single phrase and I'm using Contains() to do this. Up until today, when I noticed that the find method isn't working correctly.
So I'd like to be able to search each of the fields where there is any match. I've done some searching on Google and through SO and found suggestions of using Any()? Does anyone have any suggestions?
var l = _getData().Select(_marshallData).ToList();
return l.Where(x => x.Name.Contains(what) || x.Pumpkin.Contains(what) || x.Orange.Contains(what) || x.Tomato.Contains(what)).ToList();
Please excuse the stupid field names, I've had to change them for confidentiality.
Since you're materializing the data already you could do this:
var l = _getData().Select(_marshallData).AsEnumerable();
return l.Where(x => new[] { x.Name, x.Pumpkin, x.Orange, x.Tomato }.Any(s => s.Contains(what)));
But if you're using an ORM (like Entity Framework) this trick probably won't work (since there's a good chance this can't be converted to a SQL expression). In this case, you're original solution is fine, but it would probably be better to do this before you materialize the data.
return _getData()
.Where(x =>
x.Name.Contains(what) || x.Pumpkin.Contains(what) ||
x.Orange.Contains(what) || x.Tomato.Contains(what))
.Select(_marshallData)
.AsEnumerable();
Of course the field names here might be different, since the parameter x is probably a different type. Without further information, it's up to you to write this filter correctly.
Note that in both examples, I've eliminated the calls to ToList. Unless you absolutely need the result to a List<T> this is probably unnecessary.
In my application, I have Property Setting which is of type String.Collections.Specialized.StringCollection. It contains a list of customer codes such as MSFT, SOF, IBM etc. I'm trying to use this in a Linq-to-Entities query in the where clause:
var ShippedOrders = dbcontext.Orders
.Where(s=>(s.Status.Description.Equals("Shipped") && !Properties.Settings.Default.CustomersToExclude.Contains(s.CustomerCode)));
This fails as Contains is not recognized by Linq-to-Entities with a message similar to:
"LINQ-to-Entities does not recognize the method Contains...."
How do I revise the code above to avoid this error?
A shorter path is
myProperties.Settings.Default.CustomersToExclude.Cast<string>().Contains(blah);
That's a handy trick for any situation where a collection isn't inherently LINQ-aware.
Since your question is tagged as C# 4 use a List<string> instead (StringCollection is ancient) and your query should work. Also you should resolve your list reference outside your query:
List<string> customersToExclude = ..
var ShippedOrders = dbcontext.Orders
.Where(s=>(s.Status.Description.Equals("Shipped")
&& !customersToExclude.Contains(s.CustomerCode)));
Edit:
Just copy your customers to an array and use that:
var customerstoExclude = new string[Properties.Settings.Default.CustomersToExclude.Count];
myProperties.Settings.Default.CustomersToExclude.CopyTo(customerstoExclude, 0);
This is answered in a related question. EF4 apparently supports Contains directly, though, so that'd be my prefered solution... :)
I'm writing a little library to help building SQL requests (only doing SELECTs for the moment) but I'm not satisfied with an aspect of the syntax, here's an exemple to explain:
var db = FluentDb.WithConnectionString("SqlCeTest");
var query = db.From("Customers")
.Where(FS.Col("Age") > 18 & FS.Col("Name").StartsWith("L"))
.OrderBy("BirthDate")
.Select("Name", "Age", "BirthDate");
var customers = query.ToList((r) => new
{
Name = r.Get<string>("Name"),
Age = r.Get<int>("Age"),
BirthDate = r.Get<DateTime?>("BirtDate")
});
The part I'd like to improve is the FS.Col("ColumnName"), it's supposed to stand for FluentSql.Column (return a new FluentColumn(columnName)), but I find it a bit long in that context, what I'd really like is to be able to use just Col("ColumnName")...
Do anybody see a trick I could use to achieve that, or another syntax idea?
My ideas:
Extension method on string: Where("Name".Col() == "Jon")
Lambda expression with factory object using indexer: .Where(c => c["Name"] == "Jon")
Anyone see something better/shorter/nicer?
Edit:
my second idea looks good but there's a downside if i use it in another context:
I sometime need to use FluentColumns in Select (or OrderBy, or GroupBy) statements like that:
query.Select(FS.Col("Name").As("Customer"), FS.Col("OrderId").Count().As("OrdersCount"));
I would have to repeat the 'c => ' for each column...
A twist on your second option (which is pretty good) would be to use a dynamic expandoobject in the lambda instead of a string indexer.
http://blogs.msdn.com/b/csharpfaq/archive/2009/10/01/dynamic-in-c-4-0-introducing-the-expandoobject.aspx
Just for information, I decided to go with an indexer syntax on the FluentDb instance:
db["Customer", "AddressId"] mean column AddressId of table Customer,
an alternative syntax is available: db["Customer"]["AddressId"]
So in the end, it's gonna be (I still need to find a trick to make the Column declaration without table nice):
.Where(db["Customer", "Name"] == "Jon")