I have a listbox that I am trying to populate with the result of a SQL Server query via a Entity Framework linq/lambda query. I am feeding the query with a value from a combobox. I keep getting lot of errors like the following: Unable to create a constant value of type 'System.Object'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.
Any suggestions on how to fix this? I just want two fields to populate in a grid
var pAt = ent.Patterns.Where(p => p.Case_Id == (cbCase.SelectedItem as Case).Case_Id).Select(x => new Pattern{ PatternID = x.PatternID, Pattern1 = x.Pattern1 });
listBox1.DataSource = pAt;
listBox1.ValueMember = "PatternID";
listBox1.DisplayMember = "Pattern1";
Try this instead :
var pAt = ent.Patterns.AsEnumerable()
.Where(p => p.Case_Id == ((Case)cbCase.SelectedItem).Case_Id)
.Select(x => new Pattern{ PatternID = x.PatternID, Pattern1 = x.Pattern1 });
Hope this will fix your issue.
Separate the code parts from the SQL parts. Entity Framework can't necessarily construct an SQL query using code objects, but you can usually work around it. Eg:
var caseId = (cbCase.SelectedItem as Case).Case_Id;
var pAt = ent.Patterns.Where(p => p.Case_Id == caseId)
.ToArray()
.Select(x => new Pattern { PatternID = x.PatternID, Pattern1 = x.Pattern1 });
Related
Linq newbie here, struggling with my first GroupBy query.
I have a list of objects of type KeywordInstance which represents a keyword, and the ID of the database record to which the keyword was applied.
Keyword RecordID
macrophages 1
macrophages 2
cell cycle 3
map kinase 2
cell cycle 1
What I want is a collection of all keywords, with a list of the RecordIDs to which each keyword was applied.
Keyword RecordIDs
macrophages 1, 2
cell cycle 1, 3
map kinase 2
I tried using Linq to get it into a new object. I only managed to get the distinct keywords.
var keywords = allWords
.GroupBy(w => w.keyword)
.Select(g => new {keyword = g.Key});
The problem is that I can't seem to get the values of g in any way. g is of the type IGrouping<String, KeywordInstance> and by documentation, it only has the property Key, but not even the property Value. All the examples I have seen on the Internet for groupby just tell me to select g itself, but the result of
var keywords = allWords
.GroupBy(w => w.keyword)
.Select(g => new {keyword = g.Key, RecordIDs = g});
is not what I want.
Any try to get something out of g fails with the error message System.Linq.IGropuing<string, UserQuery.KeywordInstance> does not have a definition for [whatever I tried].
What am I doing wrong here?
I think you are close to you solution.
var keywords = allWords
.GroupBy(w => w.keyword)
.Select(g => new
{
keyword = g.Key,
RecordIDs = g.Select(c => c.ID)
});
Just Select the records you need.
The reason you are seeing the Keyword-column as well as the ID-column, is becuase it's part of g
var keywords = allWords.GroupBy(w => w.keyword);
foreach (var itm in keywords)
{
var list = itm.ToList();
//list returns all of the original properties/values objects from allwords.
//itm.key returns w.keyword
}
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 have a EF query in which i'm using lambda expressions, when i try to get the difference between two dates, it throws me exception
The specified type member 'Date' is not supported in LINQ to Entities. Only initializers, entity members, and entity navigation properties are supported.
my query is
var unApprovedLeaves = db.Leaves.Where(l => l.Status.Id == 1 && ((System.DateTime.Now.Date - l.ToDate.Date).TotalDays)==0)
.Include("Employee")
.Include("Employee.Manager")
.ToList();
can anyone tell me how do i get this thing right?
You must use SqlFunctions helper from System.Data.Objects.SqlClient. Try this:
var today = DateTime.Now.Date;
var unApprovedLeaves = db.Leaves.Where(l => l.Status.Id == 1 &&
(SqlFunctions.DateDiff("day", today, l.ToDate))==0)
.Include("Employee")
.Include("Employee.Manager")
.ToList();
In Entity Framework it is recomended to use DbFunctions helper from System.Data.Entity
Try this:
var today = DateTime.Now.Date;
var unApprovedLeaves = db.Leaves.Where(l => l.Status.Id == 1 &&
(DbFUnction.DiffDays(today, l.ToDate))==0)
.Include("Employee")
.Include("Employee.Manager")
.ToList();
I have a LINQ query where I want to select and read the p.Api value.
var api = DataAccessNew.Instance.dcServers.Where(p => p.Ip == IpAddress).Select(p => p.Api);
How do I read the p.Api value?
I have tried api.ToString() but I get SQL instead of actual column value.
You are getting an IEnumerable<> back (and your ToString call is showing you the value of that expression).
If you are expecting a single value, do this:
var api = DataAccessNew.Instance.dcServers
.Where(p => p.Ip == IpAddress)
.Select(p => p.Api)
.Single();
You might be interested to read about the other methods like Single(): SingleOrDefault, First, FirstOrDefault. Which one you used depends on whether you are expecting a single or multiple values returned (Single vs. First) and what you want to happen if there are no values (the *Default methods will return the type default instead of throwing an exception).
Or if you want to look at all the returned values:
var api = DataAccessNew.Instance.dcServers
.Where(p => p.Ip == IpAddress)
.Select(p => p.Api);
foreach (var apiValue in api)
{
// apiValue will have the value you're looking for.
}
Try this snippet of code:
string apiValue = api.FirstOrDefault().ToString();
your syntex seems ok..
By the way try this
string api =DataAccessNew.Instance.dcServers.Where(p => p.Ip == IpAddress).Select(p => p.Api).FirstOrDefault();
if p.Ip is a unique key in your table you could try to add .FirstOrDefault() after your Linq query.
public string getselectedvalue(ListBox l)
{
string vtext="",vval="";
var selectedQueryText = l.Items.Cast<ListItem>().Where(item => item.Selected);
var selectedQueryVal = l.Items.Cast<ListItem>().Where(item => item.Selected).Select(item => item.Value);
vtext= String.Join("','", selectedQueryText ).TrimEnd();
vval= String.Join("','", selectedQueryVal ).TrimEnd();
return v;
}
I am trying to use LINQ to create a Dictionary<string, List<CustomObject>> from a List<CustomObject>. I can get this to work using "var", but I don't want to use anonymous types. Here is what I have
var x = (from CustomObject o in ListOfCustomObjects
group o by o.PropertyName into t
select t.ToList());
I have also tried using Cast<>() from the LINQ library once I have x, but I get compile problems to the effect of it being an invalid cast.
Dictionary<string, List<CustomObject>> myDictionary = ListOfCustomObjects
.GroupBy(o => o.PropertyName)
.ToDictionary(g => g.Key, g => g.ToList());
I cannot comment on #Michael Blackburn, but I guess you got the downvote because the GroupBy is not necessary in this case.
Use it like:
var lookupOfCustomObjects = listOfCustomObjects.ToLookup(o=>o.PropertyName);
var listWithAllCustomObjectsWithPropertyName = lookupOfCustomObjects[propertyName]
Additionally, I've seen this perform way better than when using GroupBy().ToDictionary().
For #atari2600, this is what the answer would look like using ToLookup in lambda syntax:
var x = listOfCustomObjects
.GroupBy(o => o.PropertyName)
.ToLookup(customObject => customObject);
Basically, it takes the IGrouping and materializes it for you into a dictionary of lists, with the values of PropertyName as the key.
This might help you if you to Get a Count of words. if you want a key and a list of items just modify the code to have the value be group.ToList()
var s1 = "the best italian resturant enjoy the best pasta";
var D1Count = s1.ToLower().Split(' ').GroupBy(e => e).Select(group => new { key = group.Key, value = group.Count() }).ToDictionary(e => e.key, z => z.value);
//show the results
Console.WriteLine(D1Count["the"]);
foreach (var item in D1Count)
{
Console.WriteLine(item.Key +" "+ item.Value);
}
The following worked for me.
var temp = ctx.Set<DbTable>()
.GroupBy(g => new { g.id })
.ToDictionary(d => d.Key.id);