If I have a structure like this
Albums
- Album
- Discs
- Tracks
and I want to order a collection of albums by the title of the first track on the first disc.
Is there something similar to the following I could do (keeping in mind I need to use the OrderBy extension method that accepts a string)?
albums.OrderBy("Discs[0].Tracks[0].Title")
I need to be able to sort using a string expression thus the need to use the OrderBy method i.e. albums.OrderBy("Track[0].Title"). The reason for this is our custom framework uses a sort expression (e.g. "Title") passed back from a GridView which is looked up in a dictionary (e.g. "Track[0].Title") to get the correct order by clause. That is, the field and direction of sorting is dynamically determined at runtime.
or
albums.OrderBy("Discs.First().Tracks.First().Title")
Untested, but how about:
var query = from album in albums
let disc = album.Discs.First()
let track = disc.Tracks.First()
orderby track.Title
select album;
LINQ has two ways to query "from . in .." and Lambda expressions. They way you were almost writing it looked Lambda-ish. Here would be the Lambda expression:
albums.OrderBy(a=>a.Discs.First().Tracks.First().Title)
I used variable 'a' to indicate album but you can use any variable, this is identical to the first expression:
albums.OrderBy(album=>album.Discs.First().Tracks.First().Title)
or you can use the from obj in obj form as mention in the other answers.
How about this, in order to satisfy your need for an initial query that does not perform the sorting? This uses anonymous types to store the album information, plus the name of the first track so you can sort on it later.
var query = from album in albums
let disc = album.Discs.First()
let track = disc.Tracks.First()
select new { Album = album, FirstTrack = track.Title };
var sortedQuery = from album in query
order by album.FirstTrack
select album.Album;
Sorry people,
It looks like the OrderBy method that I am asking about and trying to use is specific to the ORM (genom-e) that we are using and is not reflected on the .net Queryable or IEnumerable classes (unlike the majority of genom-e's LINQ functionality). There is no OrderBy overload that accepts a string in .net, this is specific to genom-e.
Those of you using .net encountering a similar problem should probably give either of the above two answers a try.
Related
I am writing a reporting system which is flexible. As a part of it I create SQl statements by concatenating like
sql=" select * from a_v where ename=1 "
I want to know How I can use
db.Database.SqlQuery(sql)
to return collection of anonymous records so it is truly flexible.
I can't find a way to do it as it seems to be strongly typed.
Can it be made to return anonymous type records . An example would be great
I may have interpreted your goal incorrectly, but it sounds to me that you want to use projections. You can return lists of anonymous types from Linq. An example would be:
var anonymousListOfBoxes =
from b in CustomerBoxes
select new {
b.Customer,
b.BoxID,
b.Barcode
};
now, anonymousListOfBoxes will be a System.Linq.IQueryable<(anonymous)>. Each item will have 3 properties - Customer, BoxID and Barcode. The list will not be a collection of CustomerBoxes as it would be if you did not use a projection with "select".
I'm trying to implement a tagging system with C# entity framework. I cannot get the query required for the case that two or more tags are expected to all be present to return a result. I have a many to many relationship (just FKs, DB first) and I am attempting to get an object when all selected tags exist. Object - LookupTable - Attributes.
I parse the selected tags into a list and then try to get only those objects for which all tags in this list are present. It appears to result in what I'd expect from an "Any" operator, not the "All".
List<string> intersectTags = new List<string>();
foreach (object i in ef.objects.Where(o => o.Attributes.All(attribute =>
intersectTags.Contains(attribute.AttributeNK))))
Update: Also needed to get instances where ef.Object had more tags than intersectTags. Filtering for instances where intersectTags is a subset of Object.Attributes.
Your code fails in case your Attributes is a subset of selected tags.
If you are looking to match when intersectTags is a subset of o.Attributes, try reversing the check.
Unfortunately, Linq to Entity does not support this kind of syntax, we need ToList() to load the objects and perform Linq To Objects.
It should work but there is a performance implications (I'll post an update if I have a better solution):
List<string> intersectTags = new List<string>();
foreach (object i in ef.objects.ToList().Where(intersectTags.All(tags =>
o.Attributes.Any(attribute => attribute.AttributeNK == tags))))
I don't know if I understood well, if so I can give a solution in plain SQL. You have to lookup for all the records that contain one of the requested tag and then group them by the productId with the clause HAVING COUNT equals the number of tags you are passing.
SELECT ProductId FROM ProductTag
WHERE TagId IN (2,3,4)
GROUP BY ProductId
HAVING COUNT(*) = 3
Here's a demo:
http://sqlfiddle.com/#!3/dd4023/3
I'm sorry, currently I cannot give you an implementation in EF (don't have Visual Studio with me), I did something similar for LINQ TO SQL and it uses the PredicateBuilder class, you can find it here:
http://www.codeproject.com/Articles/36178/How-to-manage-product-options-with-different-price
Paolo
I've been looking at Dynamic Linq today (installed into VS via NuGet)...but all the examples I have found so far assume OrderBy is to be done on a known property or column name; however I am trying to OrderBy a field which is not strongly typed; but actually a key value of a row object which is derived from a Dictionary; e.g.
class RowValues : Dictionary<string, string>
{
...
}
So the list to be ordered is specifically a list of RowValues objects, filled with Name,Value pairs. For a given list of RowValues, the OrderBy field could by any of keys of the named value pairs entries (fyi: I want the orderby field to be specified in an xml config file ultimately so the ordering can be changed without re-deployment of binaries etc).
I've got a hunch the solution lies in writing a custom ordering function passed to the OrderBy??? This function would obviously know how to get a specific value from the RowValues object given a field name from the xml config....?? The answers I have seen so far show passing a string which contains a custom order by clause into the OrderBy, which is close to where I want to be, but how in my case would the runtime know where to find the fields referred to in the OrderBy string??
Input will be very much appreciated, or have I completely misunderstand the Dynamic Linq functions?
If you're using dynamic LINQ, it would just be:
var sortColumn = GetConfigValue(...);
var sorted = RowValues.OrderBy(sortColumn);
You could of course use a concatenated string to create a multiple sort ("column1, column2 DESC"). As far as I'm aware, there's no custom sort function unless you're using regular LINQ.
Also, I would make sure you know the performance characteristics of Dynamic LINQ.
Edit:
Is this what you're looking for? This will order it based on the value of the "Key" entry in the dictionary. If you need multiple sort by-s, you can use it in a loop with .ThenBy()
void Main()
{
List<RowValues> v = new List<RowValues>();
var key = "Key"; //GetFromConfig();
var v1 = new RowValues();
v1.Add("Key", "1");
v1.Add("3", "5");
var v2 = new RowValues();
v2.Add("Key", "3");
v2.Add("2", "2");
var v3 = new RowValues();
v3.Add("Key", "2");
v3.Add("2", "2");
v.Add(v1);
v.Add(v2);
v.Add(v3);
v.OrderBy(r => r[key]).Dump();
}
class RowValues : Dictionary<string, string>
{
}
Kyle, thanks again. Apologies for late reply, I have moved on from this issue now but out of interest and courtesy I wanted to come back and agree your code is much closer to where I wanted to get to, but we have lost the dynamic linq aspect. So, where you are calling the OrderBy and ordering on the key, I would want to pass a string containing the order command e.g "r[key] desc". The reason being I would want to leave the determination as to which direction to order until runtime. I suspect ths would be accomplished using an expression tree possibly? e.g: here
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... :)
Can anyone help?
I have a linq query which is embedded inside a extension method, it was working as v.RentalStatus was a String. I am now using a Group on my original query (the query is quite complex so i won't put it here).
The importante thing is that v.RentalStatus = IEnumerable hence it can contain things like
A (meaning active)
R (meaning rented)
U (unavailable)
etc - many more
I create a list of what i would like to get back and store this in statusStringList, so for example lets say the list contains A and R
This is my code from before when the v.RentalStatus was just a string, can anyone tell me how i can modify this to work.
var statusStringList = rentalStatus.ToList().ConvertAll<string>(st => st.GetStringValue());
return from v in qry
where statusStringList.Contains(v.RentalStatus)
select v;
If it helps this is part of my query which returns the RentalStatus - its part of a group query but the RentalStatus is not in the group by
RentalStatus= g1.Select( j => j.IdRentalStatus).Distinct(),
g1 is my group by, so if you imagine there are 10 "A", 5 "U" .. then it would return an ienumerable of A and U ... as i am using Distinct. Not 10 As and 5 Us
I hope i have explained it well, please tell me if i haven't
I would appreciate any help from anyone ..
thanks
EDIT
This is my extension signature but not that it matters.
public static IQueryable<Rentals> WithStatus(this IQueryable<Rentals> qry, IList<Contants.Statuses> rentalStatus)
{
EDIT
As mentioned previously when v.RentalStatus was a string it was working but now its IEnumerable - hence a collection.. and it errors with this
Argument '1': cannot convert from 'System.Collections.Generic.IEnumerable<string>' to 'string'
If RentalStatus has changed from a string to a IEnumerable<string> then your comparing 2 list... I think this should work:
return from v in qry
where v.RentalStatus.Any(status => statusStringList.Contains(status))
select v;
This should give you any rentals that have a status that is in the list you are providing
Edit:
Yeah I would spend some time learn lambda expressions. Seems like they are being used more and more and with good reason. Here are a few links for tutorials:
An Extensive Examination of LINQ: Lambda Expressions and Anonymous Types
.NET Lambda Expressions – Resources
"WHERE" RentalStatus = Containing any
of itself - arrgghh -
Is that true? I thought the list of rentalStatuses is a parameter in your method. I was thinking your query basically would allow me to get all the rentals that have a status that matches any of the list that I specified. One list lives on your Rental object and the other is the one I pass in...
As to why the order in mine worked. I have some questions:
Are you using this to query a database? Are you able to look at the tsql it generates?
If so, I would look at the tsql and see what the difference is. I would have to check myself. I got lucky I guess.
You could try something like this:
where statusStringList.Any(x => v.RentalStatus.Contains(x))
I am not sure but I think that for a Contains to work in Linq to SQL it must be an array of strings (or ints or ...) and not any IEnumerable. I would thus try:
var statusStringArray = rentalStatus.ToList().ConvertAll<string>(st => st.GetStringValue()).ToArray();
return from v in qry
where statusStringArray.Contains(v.RentalStatus)
select v;
There might be other issues though, I did not look that much.
Try this:
return from v in qry
where rentalStatus.Any( r => r.IdRentalStatus == v.RentalStatus)
select v;