I assume I need to use the method call syntax instead of the query expression form, and I know the basics of grouping in the latter. Maybe some gurus can give caveats and advice on using group fields and aggregates obtained at runtime from a configuration, for use in a reporting like structure.
Have you looked at Dynamic Linq? It should do what you want. Have a look at this post from scottgu's blog.
If your data is in xml, linq to xml would allow you to write queries against it in which the certain inputs are strings.
For example:
System.Xml.Linq.XElement myData = GetData();
System.Xml.Linq.XElement result = new XElement("Result",
myData.Elements("Customer")
.GroupBy(e => e.Attributes("Name"))
.Select(g => new XElement("CustomerResult",
new XAttribute("Name" = g.Key,
new XAttribute("Count" = g.Count(),
new XAttribute("MinDate" = g.Min(e => e.Date)
)
);
Related
I want to hydrate a collection of entities by passing in a List of Ids and also preserve the order.
Another SO answer https://stackoverflow.com/a/15187081/1059911 suggested this approach to hydrating the entities which works great
var entities = db.MyEntities.Where(e => myListOfIds.Contains(e.ID)).ToList();
however the order of entities in the collection is different from the order of Ids
Is there a way to preserve the order?
May be that helps:
var entities = db.MyEntities
.Where(e => myListOfIds.Contains(e.ID))
.OrderBy(e => myListOfIds.IndexOf(e.ID)).ToList();
EDIT
JohnnyHK clarified that this will not work with LINQ to Entities. For this to work you need to order IEnumerable instead of IQueryable, since IQueryProvider don't know how to deal with local list IndexOf method when it sends query to server. But after AsEnumerable() OrderBy method deals with local data. So you can do this:
var entities = db.MyEntities
.Where(e => myListOfIds.Contains(e.ID))
.AsEnumerable()
.OrderBy(e => myListOfIds.IndexOf(e.ID)).ToList();
Entity Framework contains a subset of all of the LINQ commands so you won't have all the commands that LINQ to Objects has.
The following approach should give you your list of MyEntities in the same order as supplied by myListOfIds:
var entities = myListOfIds.Join(db.MyEntities, m => m, e => e.ID, (m,e) => e)
.ToList();
am a newbie in linq.. am stuck with one scenario. ie,
i have to sort the search results based on user input.
user inputs are Last Name, First Name and Title. for input 3 drop downs are there and i have to sort result based on the values selected.
i tried
order = Request["orders"].Split(',');
var param = order[0];
var p1 = typeof(Test).GetProperty(param);
param = order[1];
var p2 = typeof(Test).GetProperty(param);
param = order[2];
var p3 = typeof(Test).GetProperty(param);
model.Test = (from tests in model.Test
select tests).
OrderBy(x => p1.GetValue(x, null)).
ThenBy(x => p2.GetValue(x, null)).
ThenBy(x => p3.GetValue(x, null));
but it doesn't works.
i want qry like this
from tests in model.Test
select tests).OrderBy(x => x.lastname).
ThenBy(x => x.firstname).ThenBy(x => x.Title);
order[0]== lastname but how can i use it in the place of OrderBy(x => x.order[0])..?
Thanks in advance.
i solved my case as follows
// list of columns to be used for sorting
List<string>order = Request["orders"].Split(',').ToList();
//map the column string to property
var mapp = new Dictionary<string, Func<Test, string>>
{
{"FirstName", x => x.FirstName},
{"LastName", x => x.LastName},
{"SimpleTitle", x => x.SimpleTitle}
};
//user inputted order
var paras = new List<Func<Test, string>>();
foreach (var para in order)
{
if(!string.IsNullOrEmpty(para))
paras.Add(mapp[para]);
}
//sorting
model.Test= model.Test.OrderBy(paras[0]).ThenBy(paras[1]).ThenBy(paras[2]);
Thanks all,
Actually you are looking for dynamic linq query than you can try out Dynamic LINQ (Part 1: Using the LINQ Dynamic Query Library)
which allow to do like this
it means you can dynamically pass string propertyname to short you collection in orderby function
You can also read about : Dynamic query with Linq
You can compose the expression (any Expression) manually from pieces and then append it to the previous part of query. You can find more info, with example in "Sorting in IQueryable using string as column name".
I am trying to select multiple columns from an entity object but I want 1 property to be distinct. I am very new to both LINQ and Entity Framework so any help will be useful.
Here is my LINQ query so far:
var listTypes = (from s in context.LIST_OF_VALUES
orderby s.SORT_INDEX
select new { s.LIST_TYPE, s.DISPLAY_TEXT });
I want s.LIST_TYPE to be distinct. I figure using the groupby keyword is what I want (maybe?) but I have not found a way to use it that works.
Thank you.
Assuming DISPLAY_TEXT matches LIST_TYPE somehow (so you don't lose any information):
var distinct = context.LIST_OF_VALUES
.OrderBy(s => s.SORT_INDEX)
.GroupBy(s => s.LIST_TYPE)
.Select(g => new { g.Key, g.First().DISPLAY_TEXT });
I have a search page where a user can enter multiple cities seperated by a comma and we need to get all the real estate properties where the city is one that is entered in the search criteria. For instance the user will enter something like this
cities = Dallas, Austin
The query I have works fine if the user enters a full city name
var cityList = new List{"Dallas", "Austin"};
var properties = Reporsitory.AsQueryable
.Where(x=> cityList.Contains(x.City))
.ToList();
However if I just enter Dal, Aus it does not work. How can I make these partial searches work. Is Dynamic LINQ the only answer? Thanks!
try this
var cityList = new List{"Dallas", "Austin"};
var properties = Reporsitory.AsQueryable
.Where(x=> cityList.Contains(y => x.City.Contains(y)).ToList();
try to search inside the string, i hope it works
I don't know specifically for nHibernate, but Linq to SQL does support this:
.Where(x=> x.StartsWith("Dal"))
var properties = Reporsitory.AsQueryable().Where(x => cityList.Count(c => x.StartsWith(c)) != 0);
Or replace StartWith to Contains...
Currently, I have the following LINQ queries. How can I merge the two queries into one. Basically, write a LINQ query to bring back the results I'd get from
IEnumerable<int> deltaList = people2010.Except(allPeople);
except in a single query.
var people2010 = Contacts.Where(x => x.Contractors
.Any(d => d.ContractorsStatusTrackings
.Any(date => date.StatusDate.Year >= 2010)))
.Select(x => x.ContactID);
var allPeople = Contacts.Where(x => x.Contractors
.Any(m => m.ContactID == x.ContactID))
.Select(x=> x.ContactID);
Thanks!
Why can you not just do Except as you are doing? Don't forget that your people2010 and allPeople variables are just queries - they're not the data. Why not just use them as they are?
If that's not acceptable for some reason, please give us more information - such as whether this is in LINQ to Object, LINQ to SQL etc, and what's wrong with just using Except.
It sounds like you're just looking for a more elegant way to write your query. I believe that this is a more elegant way to write your combined queries:
var deltaList =
from contact in Contacts
let contractors = contact.Contractors
where contractors.Any(ctor => ctor.ContractorStatusTrackings
.Any(date => date.StatusDate.Year >= 2010))
&& !contractors.Any(m => m.ContactID == contact.ContactID)
select contact.ContactID