I'm trying to find a more elegant way of pulling information from my db to my web application. Currently I pull all data in my table and use only two columns' data. It was suggested that I look into using SelectMany() to accomplish this by being able to select only the columns I need.
I'm not entirely sure how to translate the msdn example to a linq statement using a linq-to-sql db.
My current statement is this:
return db.document_library_sitefiles
.Where(item => item.SiteID == siteId)
.Select(item => item.document_library)
.GroupBy(item => item.Filename)
.Select(group => group.OrderByDescending(p=>p.Version).First())
.Where(item => !item.Filename.Contains("*")).ToList();
My current attempt, which I know is wrong, looks like this:
return db.document_library_sitefiles
.Where(item => item.SiteID == siteId)
.SelectMany(item => item.document_library, (filename, filesize)
=> new { filename, filesize })
.Select(item => new { filename = item.document_library.filename,
filesize = item.document_library.filesize })
.ToList();
Am I remotely close to getting my intended results?
Basically I want to get the data in my filename and filesize columns without pulling the rest of the data which includes file content (not my design or idea) so I'm not flooding my server with needless information just to show a simple data table of the files currently in this db.
I think you're going in the right direction. It looks like you're just changing the second query in an undesirable way. Give this a try;
return db.document_library_sitefiles
.Where(item => item.SiteID == siteId)
.Select(item => item.document_library)
.GroupBy(item => item.Filename)
.Select(group => group.OrderByDescending(p=>p.Version).First())
.Where(item => !item.Filename.Contains("*"))
.Select( item => new { filename = item.document_library.filename,
filesize = item.document_library.filesize } ).ToList();
Basically you want to keep all of the logic exactly the same as in the first query then just tack on one more select where you initialize the anonymous object to return.
In your attempt at the query you altered some of the underlying logic. You want all of the early operations to remain exactly the same (otherwise the results you return will be from a different set), you only want to transform objects in the resulting set which is why you add a select after the final where.
Cant you just append a select to you first statement?
....Where(item => !item.Filename.Contains("*"))
.Select(item => new {
item.Filename,
item.Filesize
}).ToList();
Related
How can I do a Group by filtering in a non-group by field? I'm using c# connected to a RavenDB database.
I'm new to RavenDB, and I'm trying to run a basic group-by query with no success, neither on RQL nor c#. I'm using Raven.Client lib 4.1.3
var results = await session.Query<Order>()
.Where(s => s.Date <= new DateTime(2019,1,1))
.GroupByArrayValues(x => x.OrderItems.Select(y => y.ProductName))
.Select(x => new
{
Product = x.Key,
Total = x.Sum(s => s.Itens.Sum(i => i.ItemValue))
})
.OrderByDescending(x => x.Total)
.ToListAsync();
When I run this code I got an AggregateException from the Raven.Client lib. Thanks in advance.
I solved the issue... Some strings were bad formatted (with blank spaces in the end) so the aggregate/groupby could not aggregate and sum them properly.
Interesting fact is that SQL Server (the source of my testing data) ignore this and sum all the looked alike results together. So if there is a wrong database here, is SQL Server.
I'm lost when it comes to to QueryOver in NHibernate, I'm trying to query over a database and retrive 4 values of importans, the rest are unnecessary and take up processing power.
I'm trying this:
var ext = _session.QueryOver<ExternServiceSettings>()
.Where(x => x.ExternService == ExternServiceEnum.Outlook).List();
which works fine but takes too long and returns everything in the database. then I tried:
var ext = _session.QueryOver<ExternServiceSettings>()
.Where(x => x.ExternService == ExternServiceEnum.Outlook)
.List<ExternServiceSettings>()
.Select(y => y.UserName);
However this only return the username and won't let me fetch more than one value...
All help is appreciated!
We should use .SelectList()
Check the example from doc:
var selection =
session.QueryOver<Cat>()
.SelectList(list => list
.Select(c => c.Name)
.SelectAvg(c => c.Age))
.List<object[]>();
see more here:
16.7. Projections
I am getting the following error. I googled it for more than a day but I cant find the exact solution, Please help me Thank you
ERROR: Cannot implicitly convert type
System.Collections.Generic.List<System.Collections.Generic.IEnumerable<ADCO.eJMC.EntityDataModel.ShareholderUser>>
to
System.Collections.Generic.List<ADCO.eJMC.EntityDataModel.ShareholderUser>
I used the following code
List<ShareholderUser> list = new List<ShareholderUser>();
list = dataContext.EJMCShareholderApprovals
.Include(s => s.Shareholder.ShareholderUsers)
.Where(e => e.EJMCRequestId == requestId)
.Select(s => s.Shareholder.ShareholderUsers
.Where(x => x.AccessMode == true))
.ToList();
The problem is that at the moment, you're selecting a sequence of sequences - one sequence of ShareholderUser items for each Shareholder. If you just want a list of ShareholderUser items, you need to flatten the results. That's most easily done using SelectMany, which can actually replace your Select call in this case.
List<ShareholderUser> list = dataContext.EJMCShareholderApprovals
.Where(e => e.EJMCRequestId == requestId)
.SelectMany(s => s.Shareholder.ShareholderUsers)
.Where(x => x.AccessMode == true)
.ToList();
Note how breaking the query over multiple lines makes it much simpler to read, too. Also, there's no point in initializing the list variable to a new List<ShareholderUser> if you're then immediately going to give it a different value. I've also removed the Include call, as that was unnecessary - you're explicitly selecting Shareholder.ShareholderUsers in the query, so you don't need to include it.
This should do it?
var list = dataContext.EJMCShareholderApprovals
.Include(s => s.Shareholder.ShareholderUsers)
.Where(e => e.EJMCRequestId == requestId)
.Select(s => s.Shareholder.ShareholderUsers
.Where(x => x.AccessMode == true)).ToList();
though you are doing select on to ShareHolderUsers? Are you trying to get a list of ShareHolderUsers or a list of lists of ShareHolderUsers?
.Select(s => s.Shareholder.ShareholderUsers
This question already has answers here:
List sort based on another list
(3 answers)
Closed 9 years ago.
I am building a search function which needs to return a list ordered by relevance.
IList<ProjectDTO> projects = new List<ProjectDTO>();
projects = GetSomeProjects();
List<ProjectDTO> rawSearchResults = new List<ProjectDTO>();
//<snip> - do the various search functions here and write to the rawSearchResults
//now take the raw list of projects and group them into project number and
//number of search returns.
//we will sort by number of search returns and then last updated date
var orderedProjects = rawSearchResults.GroupBy(x => x.ProjectNbr)
.Select(x => new
{
Count = x.Count(),
ProjectNbr = x.Key,
LastUpdated = x.First().UpdatedDateTime
})
.OrderByDescending(x => x.Count)
.ThenByDescending(x => x.LastUpdated);
So far so good; the "orderedProjects" variable returns my list in the correct order. However, I need the entire object for the next step. When I try to query back to get the original object type, my results lose their order. In retrospect, this makes sense, but I need to find a way around it.
projects = (from p in projects
where orderedProjects.Any(o => o.ProjectNbr == p.ProjectNbr)
select p).ToList();
Is there a LINQ-friendly method for preserving the order in the above projects query?
I can loop through the orderedProject list and get each item, but that's not very efficient. I can also rebuild the entire object in the original orderedProjects query, but I'd like to avoid that if possible.
You need to do it the other way around:
Query orderedProjects and select the corresponding items from projects:
var projects =
orderedProjects
.Select(o => projects.SingleOrDefault(p => p.ProjectNbr == o.ProjectNbr))
.Where(x => x != null) // This is only necessary if there can be
// ProjectNbrs in orderedProjects that are not in
// projects
.ToList();
You shouldn't use "Select" in the middle there as that operator transforms the object into another type and you say that you need the original object.
var orderedProjects = rawSearchResults.GroupBy(x => x.ProjectNbr)
.OrderByDescending(x => x.Count)
.ThenByDescending(x => x.First().UpdatedDateTime);
Do they come in chronological order or something? Otherwise, I'm pretty sure you want the "ThenByDescending" to be performed on the newest or oldest project update like so:
var orderedProjects = rawSearchResults.GroupBy(x => x.ProjectNbr)
.OrderByDescending(x => x.Count)
.ThenByDescending(x => x.Max(p=>p.UpdatedDateTime));
I have three tables, car_type, car_manufacturer and car_model. When the user click on the particular vehicle type they want to browse, I'd like to show them a list of available manufacturers. The problem is the list of manufacturers is not distinct or unique. So if my db has three models from Mazda, Mazda will show up on the list 3 times. This is my controller:
public ActionResult Browse(string click_string)
{
var x = carDB.Models
.Include(b => b.Manufacturer)
.Include(a => a.VehicleType)
.Where(a => a.VehicleType.TypeName == click_string);
return View(x.ToList());
}
How can I write this to remove redundant listings? This is all new to me, so go easy on me.
You have to query for Manufacturers, not for Vehicles:
var x = carDB.Models.Where(a => a.VehicleType.TypeName == click_string)
.Select(a => a.Manufacturer)
.Distinct();
It usually works well to try and avoid Distinct altogether. You want manufacturers? Get manufacturers. And determine from there which ones you need: the ones that produce models that have click_string in their type name:
carDB.Manufacturers.Where(manufacturer => manufacturer.Models
.Any(model => model.VehicleType.TypeName == click_string))
You may want to include Models and/or VehicleType, that depends on what you want to show in the view.
First try doing a .Distinct() at the end of the query, if it does not work you might need to provide a custom comparer for the .Distinct()
You should be able to use .Distinct to return the distinct elements.
var x = carDB.Models
.Include(b => b.Manufacturer)
.Include(a => a.VehicleType)
.Where(a => a.VehicleType.TypeName == click_string)
.Distinct();
add distinct
var x = carDB.Models
.Include(b => b.Manufacturer)
.Include(a => a.VehicleType)
.Where(a => a.VehicleType.TypeName == click_string)
.Select(y => y)
.Distinct();
The .Select() might be a bit verbose but without trying it in my visual studio i put it in there for saftey