I've looked at the various solutions here but none of them seem to work for me, probably because I'm too new to all this and am groping in the dark a bit. In the code below, the object "appointment" contains some basic LDAP information. From a list of such objects I want to be able to get a single record, based on employee id. I hope the code here is sufficient to illustrate. FTR, I've tried various formulations, including trying to use from and a select. All fail with the error given in the Title above.
IQueryable<appointment> query = null;
foreach(var record in results)
{
BoiseStateLdapDataObject record1 = record;
query = db.appointments.Where(x => x.student_id == record1.Values["employeeid"]);
}
if (query != null)
{
var selectedRecord = query.SingleOrDefault();
}
Try to move employee id getting out of query:
IQueryable<appointment> query = null;
foreach(var record in results)
{
var employeeId = record.Values["employeeid"];
query = db.appointments.Where(x => x.student_id == employeeId);
}
if (query != null)
{
var selectedRecord = query.SingleOrDefault();
}
Related
I have this service:
//seroiunoiweucroewr
///wercewrwerwerwer
//wcererewrwerwer
public List<UserRoleContract> GetRolePagesByUserId(long plngUserId, DisplayType displayType)
{
List<UserRoleContract> result = new List<UserRoleContract>();
using (CitiCallEntities context = new CitiCallEntities())
{
try
{
//var DisplayList = Utility.GetEnumDescriptions(typeof(DisplayType)).ToList();
//var selectValue = DisplayList.Where(i => i.Key == (byte) DisplayType.Windows).FirstOrDefault();
result = (from oUser in context.User
join oUserRole in context.UserRole on oUser.Id equals oUserRole.UserId
join oRoleRightsPage in context.RoleRightsPage.Where(i => i.IsActive == true)
on oUserRole.RoleId equals oRoleRightsPage.RoleId
join oApplicationPage in context.ApplicationPage.Where(i => i.IsActive == true)
on oRoleRightsPage.PageId equals oApplicationPage.Id
join oRole in context.Role on oUserRole.RoleId equals oRole.Id
join oEmployee in context.Employee on oUser.EmployeeId equals oEmployee.Id
join oSection in context.Section on oEmployee.SectionId equals oSection.Id
where oUser.IsActive == true && oUser.Id == plngUserId
&& oRole.IsActive == true && (((DisplayType)oRoleRightsPage.DisplayType).HasFlag(displayType))
//am getting error in has flag
// am having three display type web, windows and all
// how to overcome
select new UserRoleContract
{
UserId = oUser.Id,
RoleId = oRole.Id,
RoleName = oRole.RoleName,
PageID = oApplicationPage.Id,
PageName = oApplicationPage.PageName,
IsOPsCtrl = oRole.IsOPsCtrl,
ISOPsCtrlFor = oRole.OPsCtrlFor,
SectionId = oSection.Id,
DisplayType = oRoleRightsPage.DisplayType,
}).Distinct().ToList();
}
catch (Exception exception)
{
HandleExpcetion(exception);
//throw new CitiCallException(exception.Message);
}
}
return result;
}
I am getting Linq error in has flag conversion, how do I overcome this problem?
you are geeting error because HasFlag method is not paresent in database i.e. it might be part of language or local function in code which is not present in database.
So when query is translated it found this method is not available and that is the reason you are getting error.
one solution to avoid this error is
Brind all data from databae
Than filter than data, i.e. apply HasFlag method of it.
But this will bring all data and might decrease performance.
Example is
remove this line (((DisplayType)oRoleRightsPage.DisplayType).HasFlag(displayType) from your query
var list = querieddata //first fetch data without hasflag condition/method
.AsEnumerable() // Rest of the query in-process
.Where(oRoleRightsPage=> ((DisplayType)oRoleRightsPage.DisplayType).HasFlag(displayType))//apply condition here once fetching done
.ToList();
The HasFlag method has no equivalent in Linq to Entities which is why you get that error. You can get around it by using bitwise comparison instead of using HasFlag, for example this:
((DisplayType)oRoleRightsPage.DisplayType).HasFlag(displayType)
Becomes:
(oRoleRightsPage.DisplayType & displayType) > 0
So I'm working through a simplified example of my hoped-for database that has the following tables:
Contractors: Id, ContractorName
Types: Id, TypeName
CoverageZips: ContractorId, Zip
TypesForContractors: ContractorId, TypeId
where contractors can have many zips and types and types and zips can have many contractors (many-to-many).
I'm trying to:
do a search for contractors in a certain zip code
then load the types for those contractors.
The SQL for the first part would probably look like:
SELECT * FROM dbo.Contractors WHERE Id IN
(SELECT ContractorId FROM dbo.CoverageZips WHERE Zip = 12345)
Here's what I have for the first part in Simple.Data. It's working, but I feel like I'm missing some of the beauty of Simple.Data...
List<int> contractorIds = new List<int>();
foreach(var coverage in _db.CoverageZips.FindAllByZip(zip)) {
contractorIds.Add((int)coverage.ContractorId);
}
var contractors = new List<dynamic>();
if (contractorIds.Count > 0) {
contractors = _db.Contractors.FindAllById(contractorIds).ToList<dynamic>();
}
return contractors;
That's working ok until I try part 2:
public dynamic GetAllForZip(int zip) {
List<int> contractorIds = new List<int>();
foreach(var coverage in _db.CoverageZips.FindAllByZip(zip)) {
contractorIds.Add((int)coverage.ContractorId);
}
var contractors = new List<dynamic>();
if (contractorIds.Count > 0) {
contractors = _db.Contractors.FindAllById(contractorIds).ToList<dynamic>();
}
foreach (var contractor in contractors) {
// Exception occurs here on second iteration
// even though the second contractor was originally in the contractors variable
contractor.types = GetTypesForContractor((int)contractor.Id);
}
return contractors;
}
public dynamic GetTypesForContractor(int id) {
var types = new List<dynamic>();
if (id > 0) {
List<int> typeIds = new List<int>();
foreach (var typeForContractor in _db.TypesForContractor.FindAllByContractorId(id)) {
typeIds.Add((int)typeForContractor.TypeId);
}
if (typeIds.Count > 0) {
types = _db.ContractorTypes.FindAllById(typeIds).ToList<dynamic>();
}
}
return types;
}
I set a breakpoint and everything works ok for the first iteration showing , but is failing on the second with the following exception:
Index was out of range. Must be non-negative and less than the size of the collection.
tl;dr
I'm not sure how to properly use many-to-many relationships with Simple.Data and something weird is happening when I try my method more than once
I don't know what's happening with that exception and will investigate today.
You are missing some beauty, though. Assuming you have referential integrity configured on your database (which of course you do ;)), your methods can be written thus:
public dynamic GetAllForZip(int zip) {
var contractors = _db.Contractors
.FindAll(_db.Contractors.ContractorZips.Zip == zip)
.ToList();
foreach (var contractor in contractors) {
contractor.Types = GetTypesForContractor((int)contractor.Id);
}
return contractors;
}
public dynamic GetTypesForContractor(int id) {
return _db.ContractorTypes
.FindAll(_db.ContractorTypes.TypesForContractor.ContractorId == id)
.ToList();
}
Update!
As of 1.0.0-beta3, eager-loading across many-to-many joins is supported, so now you can do this:
public dynamic GetAllForZip(int zip) {
return _db.Contractors
.FindAll(_db.Contractors.ContractorZips.Zip == zip)
.With(_db.Contractors.TypesForContractor.ContractorTypes.As("Types"))
.ToList();
}
And that executes as a single SQL select to make your DBA happy like rainbow kittens.
Very frustrated here ...
I can usually find an answer of some kind to complex issues in .Net somewhere on the net, but this one eludes me.
I'm in a scenario where I have to convert the result of a LINQ to Entity query into a DataSet so the data can then be processed by existing business logic, and I can't find a single working solution out ther for this.
I've tried basic approaches like the EntityCommand generating a reader, but this one does not work because DataTable.Load() thorws an excpetion (the reader generated by EntityCommand does not support GetSchemaTable() ).
I've also tried more [supposedly] friendly approaches like Entity to IDataReader(http://l2edatareaderadapter.codeplex.com/), but this one throws exceptions, has very little docs, and hasn't been touched since 2008.
Another approach I found is here (http://blogs.msdn.com/b/alexj/archive/2007/11/27/hydrating-an-entitydatareader-into-a-datatable-part-1.aspx), but does not have a working copy of the code; only snippets.
I find it hard to believe that first of all MS would not have offered this backwards-compatibility item out of the box, and second, that it would not have been created by the community either.
I'm willing to look at commercial solutions as well if any are available.
Thx!
You can convert the result into a list and use the following to convert the list to a datatable.
public DataTable ConvertToDataTable<T>(IList<T> data)
{
PropertyDescriptorCollection properties =
TypeDescriptor.GetProperties(typeof(T));
DataTable table = new DataTable();
foreach (PropertyDescriptor prop in properties)
table.Columns.Add(prop.Name, Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType);
foreach (T item in data)
{
DataRow row = table.NewRow();
foreach (PropertyDescriptor prop in properties)
row[prop.Name] = prop.GetValue(item) ?? DBNull.Value;
table.Rows.Add(row);
}
return table;
}
http://social.msdn.microsoft.com/Forums/br/csharpgeneral/thread/6ffcb247-77fb-40b4-bcba-08ba377ab9db
Hope this helps
Preetam
This might not be the greatest solution, but if your scenario have only one or two table that you need to add to the DataSet, why not build them directly manually.
var result = db.YourTable; // get your Linq To Entities result.
DataSet ds = new DataSet();
DataTable tbl = new DataTable();
tbl.Columns.Add("col1", typeof(string));
tbl.Columns.Add("col2", typeof(int));
foreach (var r in result)
{
var row = tbl.NewRow();
row[0] = r.Col1;
row[1] = r.Col2;
tbl.Rows.Add(r);
}
ds.Tables.Add(tbl);
The Col1 and Col2 comes from your Linq To Entity objects, you can create all the table you need like this and return your DataSet.
This is a flexible code and should handle most of your needs:
public DataTable LINQToDataTable<T>(IEnumerable<T> varlist)
{
DataTable dtReturn = new DataTable();
// column names
PropertyInfo[] oProps = null;
if (varlist == null) return dtReturn;
foreach (T rec in varlist)
{
// Use reflection to get property names, to create table, Only first time, others will follow
if (oProps == null)
{
oProps = ((Type)rec.GetType()).GetProperties();
foreach (PropertyInfo pi in oProps)
{
Type colType = pi.PropertyType;
if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition() == typeof(Nullable<>)))
{
colType = colType.GetGenericArguments()[0];
}
dtReturn.Columns.Add(new DataColumn(pi.Name, colType));
}
}
DataRow dr = dtReturn.NewRow();
foreach (PropertyInfo pi in oProps)
{
dr[pi.Name] = pi.GetValue(rec, null) == null ? DBNull.Value : pi.GetValue
(rec, null);
}
dtReturn.Rows.Add(dr);
}
return dtReturn;
}
I am having some trouble with a linq query I am trying to write.
I am trying to use the repository pattern without to much luck. Basically I have a list of transactions and a 2nd list which contains the description field that maps against a field in my case StoreItemID
public static IList<TransactionViewModel> All()
{
var result = (IList<TransactionViewModel>)HttpContext.Current.Session["Transactions"];
if (result == null)
{
var rewardTypes = BusinessItemRepository.GetItemTypes(StoreID);
HttpContext.Current.Session["Transactions"] =
result =
(from item in new MyEntities().TransactionEntries
select new TransactionViewModel()
{
ItemDescription = itemTypes.FirstOrDefault(r=>r.StoreItemID==item.StoreItemID).ItemDescription,
TransactionDate = item.PurchaseDate.Value,
TransactionAmount = item.TransactionAmount.Value,
}).ToList();
}
return result;
}
public static List<BusinessItemViewModel>GetItemTypes(int storeID)
{
var result = (List<BusinessItemViewModel>)HttpContext.Current.Session["ItemTypes"];
if (result == null)
{
HttpContext.Current.Session["ItemTypes"] = result =
(from items in new MyEntities().StoreItems
where items.IsDeleted == false && items.StoreID == storeID
select new BusinessItemViewModel()
{
ItemDescription = items.Description,
StoreID = items.StoreID,
StoreItemID = items.StoreItemID
}).ToList();
}
return result;
However I get this error
Unable to create a constant value of type 'MyMVC.ViewModels.BusinessItemViewModel'. Only primitive types ('such as Int32, String, and Guid') are supported in this context.
I know its this line of code as if I comment it out it works ok
ItemDescription = itemTypes.FirstOrDefault(r=>r.StoreItemID==item.StoreItemID).ItemDescription,
How can I map ItemDescription against my list of itemTypes?
Any help would be great :)
This line has a problem:
ItemDescription = itemTypes.FirstOrDefault(r=>r.StoreItemID==item.StoreItemID)
.ItemDescription,
Since you are using FirstOrDefault you will get null as default value for a reference type if there is no item that satifies the condition, then you'd get an exception when trying to access ItemDescription - either use First() if there always will be at least one match or check and define a default property value for ItemDescription to use if there is none:
ItemDescription = itemTypes.Any(r=>r.StoreItemID==item.StoreItemID)
? itemTypes.First(r=>r.StoreItemID==item.StoreItemID)
.ItemDescription
: "My Default",
If itemTypes is IEnumerable then it can't be used in your query (which is what the error message is telling you), because the query provider doesn't know what to do with it. So assuming the that itemTypes is based on a table in the same db as TransactionEntities, then you can use a join to achieve the same goal:
using (var entities = new MyEntities())
{
HttpContext.Current.Session["Transactions"] = result =
(from item in new entities.TransactionEntries
join itemType in entities.ItemTypes on item.StoreItemID equals itemType.StoreItemID
select new TransactionViewModel()
{
ItemDescription = itemType.ItemDescription,
TransactionDate = item.PurchaseDate.Value,
TransactionAmount = item.TransactionAmount.Value,
CustomerName = rewards.CardID//TODO: Get customer name
}).ToList();
}
I don't know the structure of your database, but hopefully you get the idea.
I had this error due a nullable integer in my LINQ query.
Adding a check within my query it solved my problem.
query with problem:
var x = entities.MyObjects.FirstOrDefault(s => s.Obj_Id.Equals(y.OBJ_ID));
query with problem solved:
var x = entities.MyObjects.FirstOrDefault(s => s.Obj_Id.HasValue && s.Obj_Id.Value.Equals(y.OBJ_ID));
I have a variable size array of strings, and I am trying to programatically loop through the array and match all the rows in a table where the column "Tags" contains at least one of the strings in the array. Here is some pseudo code:
IQueryable<Songs> allSongMatches = musicDb.Songs; // all rows in the table
I can easily query this table filtering on a fixed set of strings, like this:
allSongMatches=allSongMatches.Where(SongsVar => SongsVar.Tags.Contains("foo1") || SongsVar.Tags.Contains("foo2") || SongsVar.Tags.Contains("foo3"));
However, this does not work (I get the following error: "A lambda expression with a statement body cannot be converted to an expression tree")
allSongMatches = allSongMatches.Where(SongsVar =>
{
bool retVal = false;
foreach(string str in strArray)
{
retVal = retVal || SongsVar.Tags.Contains(str);
}
return retVal;
});
Can anybody show me the correct strategy to accomplish this? I am still new to the world of LINQ :-)
You can use the PredicateBuilder class:
var searchPredicate = PredicateBuilder.False<Songs>();
foreach(string str in strArray)
{
var closureVariable = str; // See the link below for the reason
searchPredicate =
searchPredicate.Or(SongsVar => SongsVar.Tags.Contains(closureVariable));
}
var allSongMatches = db.Songs.Where(searchPredicate);
LinqToSql strange behaviour
I recently created an extension method for creating string searches that also allows for OR searches. Blogged about here
I also created it as a nuget package that you can install:
http://www.nuget.org/packages/NinjaNye.SearchExtensions/
Once installed you will be able to do the following
var result = db.Songs.Search(s => s.Tags, strArray);
If you want to create your own version to allow the above, you will need to do the following:
public static class QueryableExtensions
{
public static IQueryable<T> Search<T>(this IQueryable<T> source, Expression<Func<T, string>> stringProperty, params string[] searchTerms)
{
if (!searchTerms.Any())
{
return source;
}
Expression orExpression = null;
foreach (var searchTerm in searchTerms)
{
//Create expression to represent x.[property].Contains(searchTerm)
var searchTermExpression = Expression.Constant(searchTerm);
var containsExpression = BuildContainsExpression(stringProperty, searchTermExpression);
orExpression = BuildOrExpression(orExpression, containsExpression);
}
var completeExpression = Expression.Lambda<Func<T, bool>>(orExpression, stringProperty.Parameters);
return source.Where(completeExpression);
}
private static Expression BuildOrExpression(Expression existingExpression, Expression expressionToAdd)
{
if (existingExpression == null)
{
return expressionToAdd;
}
//Build 'OR' expression for each property
return Expression.OrElse(existingExpression, expressionToAdd);
}
}
Alternatively, take a look at the github project for NinjaNye.SearchExtensions as this has other options and has been refactored somewhat to allow other combinations
There is another, somewhat easier method that will accomplish this. ScottGu's blog details a dynamic linq library that I've found very helpful in the past. Essentially, it generates the query from a string you pass in. Here's a sample of the code you'd write:
Dim Northwind As New NorthwindDataContext
Dim query = Northwind.Products _
.Where("CategoryID=2 AND UnitPrice>3") _
.OrderBy("SupplierId")
Gridview1.DataSource = query
Gridview1.DataBind()
More info can be found at scottgu's blog here.
Either build an Expression<T> yourself, or look at a different route.
Assuming possibleTags is a collection of tags, you can make use of a closure and a join to find matches. This should find any songs with at least one tag in possibleTags:
allSongMatches = allSongMatches.Where(s => (select t from s.Tags
join tt from possibleTags
on t == tt
select t).Count() > 0)