I have a question of how to sort an anonymous type.
Using Linq2SQL I have the following query, which returns a list of submissions:
var submissions = EventSubmissions
.Where(s => s.EventId.Equals(eventId));
Consider the following interface (somewhat simplyfied):
public interface IQuerySorter
{
IOrderedQueryable Sort(IQueryable query);
IOrderedQueryable<T> Sort<T, U>(IQueryable<T> query, Expression<Func<T,U>> selector);
...
}
Using this interface allows me to implement a number of 'sorters', e.g. on Date, Rating or whether or not a submission has been nominated (for voting).
sortedQuery = sorter.Sort(submissions)
So far so good. A submission can be made "votable". I get the number of votes a nominated submission may have using the following query:
var withVoteCount = submissions
.Select(s => new {NumberOfVotes = s.Votes.Count(), Submission = s});
I would like to sort this new query by NumberOfVotes using my "general" sorter class, but run into the problem that the anonymous type/member does not seem to live outside the repository-method, hence I am unable to sort on it.
Any input would be greatly appreciated.
I would recommend creating a view or stored procedure using Group By and Count to get the same results as:
var withVoteCount = submissions
.Select(s => new {NumberOfVotes = s.Votes.Count(), Submission = s});
By using SQL you can tell it to order by Count of votes. Something like this (rough example):
select submissions.ID, submissions.Title, count(votes.ID) as NumberOfVotes
from submissions inner join votes on submissions.id = votes.submissionid
group by submissions.ID, submissions.Title
order by NumberOfVotes desc
After creating the sql view or stored procedure in your SQL server db, you can just drop it in the designer in Visual Studio and use it as regular class or function.
Related
I have a list of objects (say family), and each object contains a list of other non-value type object (say child). I would like to query this list and specify the where clause dynamically (during run-time).
var fselected = from f in families
from c in f.Children
where (f.FamilyAge > 15 && c.Age > 13)
select f;
The closest thing I found that would do that is Dynamic LINQ on NuGet, but beyond the simple where clause on the top level object, I can't find any examples on how to do above statement.
The only solution I can think of is to split into separate where clause for C and for F, run the c query first, then run F query on resultant data set...
don't use strings to let your users create dynamic queries on your database, that will leave you vulnerable to sql injection. Instead, expose nullable parameters to your users
public Family GetFamily(int? familyAge, int? age)
{
var families = GetAllFamilies();
if(familyAge.HasValue)
families = families.Where(x => x.familyAge = familyAge.value);
if(age.HasValue)
families = families.Where(x => x.age = age.value);
return familes.ToList();
}
Update
Despite the problems of injections when using strings to let your users query your db, you can use the Dynamic Linq Library to pass on a string as a query. But I do advise against using this.
I have a sql statement like this:
DECLARE #destinations table(destinationId int)
INSERT INTO #destinations
VALUES (414),(416)
SELECT *
FROM GroupOrder grp (NOLOCK)
JOIN DestinationGroupItem destItem (NOLOCK)
ON destItem.GroupOrderId = grp.GroupOrderId
JOIN #destinations dests
ON destItem.DestinationId = dests.destinationId
WHERE OrderId = 5662
I am using entity framework and I am having a hard time getting this query into Linq. (The only reason I wrote the query above was to help me conceptualize what I was looking for.)
I have an IQueryable of GroupOrder entities and a List of integers that are my destinations.
After looking at this I realize that I can probably just do two joins (like my SQL query) and get to what I want.
But it seems a bit odd to do that because a GroupOrder object already has a list of DestinationGroupItem objects on it.
I am a bit confused how to use the Navigation property on the GroupOrder when I have an IQueryable listing of GroupOrders.
Also, if possible, I would like to do this in one trip to the database. (I think I could do a few foreach loops to get this done, but it would not be as efficient as a single IQueryable run to the database.)
NOTE: I prefer fluent linq syntax over the query linq syntax. But beggars can't be choosers so I will take whatever I can get.
If you already have the DestinationGroupItem as a Navigation-property, then you already have your SQL-JOIN equivalent - example. Load the related entities with Include. Use List's Contains extension method to see if the desired DestinationId(s) is(are) hit:
var destinations = new List<int> { 414, 416 };
var query = from order in GroupOrder.Include(o => o.DestinationGroupItem) // this is the join via the navigation property
where order.OrderId == 5662 && destinations.Contain(order.DestinationGroupItem.DestinationId)
select order;
// OR
var query = dataContext.GroupOrder
.Include(o => o.DestinationGroupItem)
.Where(order => order.OrderId == 5662 && destinations.Contain(order.DestinationGroupItem.DestinationId));
I have seen these StackOverflow Answers but they do not produce the same results when the filtering list is in memory.
I have a list of Ids. I want to remove any IDs that exists in the database, so that I am left with a list of IDs that need to be added. In other words, I need to perform a where not in SQL query, using Linq-To-Entities. The problem is, instead of producing that SQL, these methods each produce a SQL query per list item.
var providerIds = new [] {"1130", "1", "16"};
Method 1:
var missingProviders = (from provider in providerIds
where !JobProviders.Any(p => p.JobProviderID == provider)
select provider).ToList();
Method 2:
var missingProviders = (from provider in providerIds
where !(from p in JobProviders select p.JobProviderID).Contains(provider)
select provider).ToList();
Is there a way to structure the LINQ query such that it produces the intended not in form, or are these the only solutions?
What about something like
var providersInDb = (from provider in JobProviders
where providerIds.Contains(provider.JobProviderID)
select provider.JobProviderID).ToList();
var missingProviders = providerIds.Where(p => !providersInDb.Contains(p))
Tricky. I don't have my tools in front of me, so I don't know how this will pan out exactly.
var dbProviderIds = JobProviders.Select(p => p.JobProviderId);
var allProviders = dbProviderIds.Union(providerIds).Distinct();
var missing = allProviders.Except(dbProviderIds);
On the DB, get all the provider Ids, then combine that with the in-memory ones. Then remove the ones that are known on the database.
I have a Linq to NHibernate query as follows:
var profile =
from UserProfile up in _Session.Query<UserProfile>()
.Fetch(x=>x.Messages)
where up.UserName == userName
select up.Messages;
this returns an IQueryable<IList<UserMessage>> which I then have to run a SelectMany() on. I'd prefer if I could just return an IQueryable<UserMessage> object instead, especially as the query will never return more than one user profile. Can this be done, or am I stuck with the extra step?
If you map the other side of the navigation e.g have a UserProfile property on the UserMessage class, your can start from UserMessage:
var messages =
from UserMessage um in _Session.Query<UserMessage>()
where um.UserProfile.UserName == userName
select um;
Otherwise you need to use SelectMany() to get a flattened out list.
Could you query the messages table directly and use the reverse association?
IQueryable<Message> messages = ...;
var filtered = from m in messages
where m.UserProfile.UserName == userName
select m;
Also, if you're willing to forgo query syntax you could make this shorter with:
var profile = _Session.Query<UserProfile>()
.Where(up => up.UserName == userName)
.SelectMany(up => up.Messages);
I'm currently using EF Code-First, and I'd like to SELECT data from many tables in the database. This query is a customizable query, and hence I can't predict what kind of data I will be retrieving.
At first, when I tried running ctx.Database.SqlQuery<string>(sql, param), I ran into an exception when facing a DateTime value. I'd like to do this without casting it on the server side.
Does anybody have any idea how I can go about doing it? It can be in LINQ, LINQ-SQL, or purely SQL--so long as it gets the job done! Thanks guys...
You will not get it. Linq-to-entities will not make transformation to list of strings. Your best chance is executing normal queries and do conversion and transformation your application.
Argument that you don't know which columns user selects just means you need more dynamic solution - Linq-to-entities is not a good tool for you (except if you try to use Dynamic Linq or build expression trees manually). Use ESQL or SQL directly.
When selecting data from many tables, use anonymous types to encapsulate the properties(fields) you want to select from these tables into a new entity, something like:
var query = _db.Categories.Join(
_db.Products,
c => c.CategoryId,
p => p.CategoryId,
(category, product) =>
new
{
ProductName = product.Name,
CategoryName = category.Name,
ExpiryDate = product.ExpiryDate
});
You can achieve string values by casting your data fields to string in this way:
var query = _db.Categories.Join(
_db.Products,
c => c.CategoryId,
p => p.CategoryId,
(category, product) =>
new
{
ProductName = product.Name.toString(),
CategoryName = category.Name.toString(),
ExpiryDate = product.ExpiryDate.toString()
});