I have a database that looks like this:
tbl_Seminar
ID
isActive
tbl_SeminarFees
ID
seminar_id -- foreign key
fee_text
I want to get all seminars that are active (isActive ==1) and a list of the fees associated with that seminar. Each Seminar may have n records in tbl_SeminarFees that are its fees. I am able to return a linq structure that returns me a list of objects that look like this {seminar, SeminarFee} but I wanted to create a nested structure that looks like this:
{seminar, List<SeminarFee>}
What should my linq query look like?
here is my linq currently:
var results = from s in context.Seminar
join p in context.SeminarFees on
s.ID equals p.SeminarID
where s.IsActive == 1
select new
{
Seminar = s,
Fees = p
};
How do I change this to get a list of these: {seminar, List<SeminarFee>}
Thanks
UPDATE
#lazyberezovsky gave me a good idea to use a group join and into another variable. But then how do I loop through the result set. Here is what I have now:
foreach (var seminarAndItsFeesObject in results)
{
//do something with the seminar object
//do something with the list of fees
}
This however gives me the following error:
Argument type 'SeminarFees' does not match the
corresponding member type
'System.Collections.Generic.IEnumerable`1[SeminarFees]'
What am I doing wrong?
Thanks
You can use group join which groups inner sequence items based on keys equality (a.k.a. join..into) to get all fees related to seminar:
var results = from s in context.Seminar
join f in context.SeminarFees on
s.ID equals f.SeminarID into fees // here
where s.IsActive == 1
select new
{
Seminar = s,
Fees = fees
};
You can't call ToList() on server side. But you can map results on client later.
BTW You can define navigation property Fees on Seminar object:
public virtual ICollection<SeminarFee> Fees { get; set; }
In this case you will be able load seminars with fees:
var results = context.Seminar.Include(s => s.Fees) // eager loading
.Where(s => s.IsActive == 1);
var results = from s in context.Seminar
join p in context.SeminarFees on s.ID equals p.SeminarID
where s.IsActive == 1
group p by s into grouped
select new {
Seminar = grouped.Key,
Fees = grouped.ToList()
};
Related
In the following code:
var finalArticles =
from domainArticle in articlesFoundInDomain
join articleCategoryVersion in dbc.ArticlesCategoriesVersions
on domainArticle.ArticleID equals articleCategoryVersion.ArticleID
join articleCategory in dbc.ArticleCategories
on articleCategoryVersion.CategoryID equals articleCategory.CategoryID
where articleCategory.ParentID == 52
group articleCategory by articleCategory.CategoryID
into newArticleCategoryGroup
I understand that the group clause should be returning an IEnumerable where k is the Key, in this case CategoryID.
I think I'm misunderstanding Linq at this point because I assume that for each 'k' there should be a list of articles in 'v', but I don't understand the mechanisms or terminology or something. When I try to project this statement into a new anonymous object I don't seem to get any articles... where are they?
Edit:
Okay so I've got a piece of code that is working, but unfortunately it's hitting the SQL server multiple times:
var articlesAssociatedWithKnowledgeTypes =
from categories in dbc.ArticleCategories
join categoryVersions in dbc.ArticlesCategoriesVersions
on categories.CategoryID equals categoryVersions.CategoryID
join articles in articlesFoundInGivenDomain
on categoryVersions.ArticleID equals articles.ArticleID
where categories.ParentID == 52 && articles.Version == categoryVersions.Version
select new
{
ArticleID = articles.ArticleID,
ArticleTitle = articles.Title,
ArticleVersion = articles.Version,
CategoryID = categories.CategoryID,
CategoryName = categories.Name
} into knowledgeTypesFlat
group knowledgeTypesFlat by new { knowledgeTypesFlat.CategoryID, knowledgeTypesFlat.CategoryName } into knowledgeTypesNested
select new
{
CategoryID = knowledgeTypesNested.Key.CategoryID,
CategoryName = knowledgeTypesNested.Key.CategoryName,
Articles = knowledgeTypesNested.ToList()
};
I thought the ToList() on Articles would sort that out but it doesn't. But, the code works although I'm not sure if this is optimal?
The grouping returns an enumeration of IGroupings. IGrouping<K, V> itself implements IEnumerable<V>. Think of each group as an enumerable of all the members of that group plus an extra property Key
In your first query you are showing a group by and the second one is a group join, both return different results. The group by returns an IEnumerable<IGrouping<TKey, TElement>>. To get the result you're expecting you could group by CategoryId and CategoryName and project as I show below:
var finalArticles =
from domainArticle in articlesFoundInDomain
join articleCategoryVersion in dbc.ArticlesCategoriesVersions
on domainArticle.ArticleID equals articleCategoryVersion.ArticleID
join articleCategory in dbc.ArticleCategories
on articleCategoryVersion.CategoryID equals articleCategory.CategoryID
where articleCategory.ParentID == 52
group articleCategory by new{ articleCategory.CategoryID,articleCategory.CategoryName}
into g
select new {CatId=g.Key.CategoryID, CatName=g.Key.CategoryName,Articles =g.ToList() };
When you need the grouped elements you can call ToList or ToArray as I did above
Your finalArticles query results in a IEnumerable<IGrouping<int, Article>> (assuming CategoryID is int and your articles are of type Article).
These IGrouping<int, Article> provides a Key property of type int (your CategoryID and also the IEnumerable<Article> representing the sequence of articles for that CategoryID.
You can turn this for example into a Dictionary<int, List<Article>> mapping CategoryIDs to the lists of articles:
var dictionary = finalArticles.ToDictionary(group => group.Key, group => group.ToList());
or to a list of categories containing articles:
var categories = finalArticles.Select(group => new {
CategoryID = group.Key,
Articles = group.ToList()}).ToList();
Update after your comment:
var finalArticles =
from domainArticle in articlesFoundInDomain
join articleCategoryVersion in dbc.ArticlesCategoriesVersions
on domainArticle.ArticleID equals articleCategoryVersion.ArticleID
join articleCategory in dbc.ArticleCategories
on articleCategoryVersion.CategoryID equals articleCategory.CategoryID
where articleCategory.ParentID == 52
group articleCategory by new {articleCategory.CategoryID, articleCategory.Name}
into newArticleCategoryGroup
select new
{
CategoryID = newArticleCategoryGroup.Key.CategoryID,
CategoryName = newArticleCategoryGroup.Key.Name,
Articles = newArticleCateGroup.ToList()
}
I am implementing a controller and I need to get all staff members which have a certain RiskTypeID, which will be selected by the user when they click on Navigation Item.
Here is how I would create the joins in SQL
SQL
Select
RTHG.RiskTypeID,
SM.FullName
From RiskTypeHasGroup RTHG
Inner join RiskGroup RG On RTHG.RiskGroupID = RG.ID
Inner join RiskGroupHasGroupMembers RGHGM ON RG.ID = RGHGM.RiskGroupID
Inner Join GroupMember GM ON RGHGM.GroupMemberID = GM.ID
Inner Join GroupMemberHasStaffMember GMHSM ON GM.ID = GMHSM.GroupMemberID
Inner Join StaffMember SM ON GMHSM.StaffMemberID = SM.ID
Where RTHG.RiskTypeID = 1
I’ve pulled back data before using Linq and lambda but only using simple expressions, I now need to be able to make a call which will bring back the same data as the sql outlined above, I’ve searched online but can’t find anything similar to my requirement.
Here is my Controller, I placed comments inside as guidance
Controller
public ActionResult ViewRiskTypes(int SelectedRiskTypeID)
{
var RiskTypes = _DBContext.RiskTypes.ToList(); // Get all of the current items held in RiskTypes tables, store them as a List in Var RiskTypes
var ViewModel = new List<RiskTypeWithDetails>(); // Create colletion which holds instances of RiskTypeWithDetails and pass them to the ViewModel
var Details = new RiskTypeWithDetails(); // Create a new instance of RiskType with details and store the instance in var Details
foreach (var RiskType in RiskTypes) // Loop through each Item held in var RiskTypes
{
Details.RiskTypes.Add(new RiskTypesItem { ID = RiskType.ID, Description = RiskType.Description }); // assign each items ID & Description to the same feilds in a new
// instance of RiskTypeItems (which is a property of RiskTypeWithDetails)
}
foreach (var RiskType in RiskTypes) // Loop through each item in RiskTypes
{
if (RiskType.ID == SelectedRiskTypeID) // Check Item ID matches SelectedRiskTypeID value
{
//var Details = new RiskTypeWithDetails();
Details.RiskTypeDescription = RiskType.Description; //assign the Risk type Descripton to RiskTypeWithDetails RiskTypeDescription Property
Details.RiskDetails = _DBContext
.RiskTypeHasGroups
//.GroupMemberTypeHasGroupMembers
.Where(r => r.RiskTypeID == SelectedRiskTypeID) // Where RiskTypeId matches Selected ID bring back following data from Db
.Select(r => new RiskDetails
{
RiskGroupDescription = r.RiskGroup.Description,
GroupMembers = r.RiskGroup.RiskGroupHasGroupMembers
.Select(v => v.GroupMember).ToList(),
//StaffMembers = r.RiskGroup.RiskTypeHasGroups
// .Join(r.RiskGroup.RiskTypeHasGroups,
// a => a.RiskGroupID , b => b.RiskGroup.ID,
// (a, b) => new {a, b})
// .Join(r.RiskGroup.RiskGroupHasGroupMembers,
// c => c.) // Dosent join as I would expect... no idea what to do here
}).ToList();
ViewModel.Add(Details); //Add all data retrieved to the ViewModel (This creates one item in the collection)
}
}
return View(ViewModel);
}
As you will see I want to get all Staff Members with a match for the selected RiskTypeID. I need some assistance in converting the above SQL to work within my controller as a lambda expression
Thanks in advance
You were on the right track with your commented out code! For starters, LINQ has two different sytaxes: query and method chain. You were using the method chain syntax and it can get really unmaintainable really quickly.
For an instance like this, query syntax is where it's at.
Here's the result:
from rhtg in _dbContext.RiskTypeHasGroup
where rhtg.RiskTypeID == 1
join rg in _dbContext.RiskGroup
on rhtg.RiskGroupID equals rg.ID
join rghgm in _dbContext.RiskGroupHasGroupMembers
on rg.ID equals rhtg.ID
join gm in _dbContext.GroupMember
on rg.ID equals gm.ID
join gmhsm in _dbContext.GroupMemberHasStaffMember
on gm.ID equals gmhsm.GroupMemberID
join sm in _dbContext.StaffMember
on gmhsm.StaffMemberID equals sm.ID
select new
{
rhtg.RiskTypeId,
sm.FullName
};
Do note, that I used .Net conventions for the different variables.
Here's some documentation on the query syntax:
https://msdn.microsoft.com/en-us/library/gg509017.aspx
You can write the exact same query in linq as follows:
var query = (from RTHG in _DBContext.RiskTypeHasGroup RTHG
join RG in _DBContext.RiskGroup on RTHG.RiskGroupID equals RG.ID
join RGHGM in _DBContext.RiskGroupHasGroupMembers on RG.ID equals RGHGM.RiskGroupID
join GM in _DBContext.GroupMember on RGHGM.GroupMemberID = GM.ID
join GMHSM in _DBContext.GroupMemberHasStaffMember on GM.ID equals GMHSM.GroupMemberID
join SM in _DBContext.StaffMember on GMHSM.StaffMemberID equals SM.ID
where RTHG.RiskTypeID == 1
select new {RTHG.RiskTypeID,SM.FullName});
I have the following two objects:
User
class User {
public int role;
}
Role
class Role {
public int id;
public string name;
}
be note that role property inside User is int and not Role, that's our limitations.
I want to join between all the users and each of his role. In the mapping objects there is no reference as you can understand, just a simple type (int).
How do I do that join statement?
It's called a theta join:
var a = (from u in session.Query<User>()
from r in session.Query<Role>()
where u.role == r.id
select new { u.Username, Role = r.name }).ToList();
Assuming you have a Username property on the User class.
Yes, this "theta join" (as I just learned this term) is very handy and let's us not worry about putting in pointless mapping relationships.
WARNING HOWEVER IN USING THIS!!! This tripped me up a lot.
Adding to the above example...
var list = new List<int>( { 2, 3 } ); // pretend in-memory data from something.
var a =
(from u in session.Query<User>()
from x in list
from r in session.Query<Role>()
where u.role == r.id
where r.id == x.id // pretend list wants to limit to only certain roles.
select new { u.Username, Role = r.name }).ToList();
THIS WILL BOMB with some NotSupported exception.
The trick is that anything coming from NHibernate Session must come LAST. So this alteration WILL work:
var a =
(from x in list
from u in session.Query<User>()
from r in session.Query<Role>()
where u.role == r.id
where r.id == x.id // pretend list wants to limit to only certain roles.
select new { u.Username, Role = r.name }).ToList();
And and BTW, you can use join as well, however you have to make sure if you have any nullable data types, that you use the .Value if you are joining to something not-nullable.
var a =
(from x in list
from u in session.Query<User>()
join r in session.Query<Role>() on u.role equals r.id
where r.id == x.id // pretend list wants to limit to only certain roles.
select new { u.Username, Role = r.name }).ToList();
And while we're at it, let's say you have a method that has some dynamic condition. In this example the 'list' which could be a list of roles to filter by, but don't filter at all if the list is not there. Well, if you do the .ToList() then you are causing this query to execute immediately. But instead you can add a condition and then execute it later:
var a =
from u in session.Query<User>()
join r in session.Query<Role>() on u.role equals r.id
where r.id == x.id // pretend list wants to limit to only certain roles.
select new { u.Username, Role = r.name, RoleID = r.id }; // Adding the Role ID into this output.
if (list != null) // assume if the list given is null, that means no filter.
{
a = a.Where(x => list.Contains(x.RoleID));
// WARNING. Unfortunately using the "theta" format here will not work. Not sure why.
}
var b = a.ToList(); // actually execute it.
var c = a.Select(x => new { x.Username, x.Role }).ToList() // if you insist on removing that extra RoleID in the output.
One last thing.. Sometimes some simple logic will fail when executed in the select new { .. } part. I don't have an explanation. In our case the logic was just converting a DB value of a uint to an Enumerator of a model. But to get around that, I just avoided doing that conversion while reading the data but saved the value. Then in a later step, after the data was loaded, I just did the conversion in another LINQ statement.
DISCLAIMER: While I wrote many of these things all the past several weeks, I did not put this code into my compiler to verify 100%.
Work on entity frame work vs2010
After execute my linq query get a list of records ,want to put this record in session .Now from session Want to get back my record list ,what to do how to get back record from a session
Linq query
public IEnumerable GetSearchUserGroupPermissionData(int userID = 0)
{
var query = from p in this.Context.CmnPermissionGroupUsers
join q in this.Context.CmnPermissionGroups on p.PermissionGroupID equals q.PermissionGroupID
join r in this.Context.CmnPermissionGroupDocs on p.PermissionGroupID equals r.PermissionGroupID
join s in this.Context.CmnUserInfoes on p.UserID equals s.UserID
join t in this.Context.CmnDocLists on r.DocListID equals t.DocListID
//join u in this.Context.CmnModuleFormCompanies on t.ModuleID equals u.ModuleID
//join v in this.Context.CmnModuleLists on u.ModuleID equals v.ModuleID
//join w in this.Context.CmnFormLists on u.FormID equals w.FormID
where p.IsDeleted == false
select new
{
RecordID = p.PermissionGroupUserRecordID,
s.UserID,
s.UserFirstName,
q.PermissionGroupName,
p.EffectiveDate,
p.StatusID,
t.DocListID,
t.DocName,
t.ModuleID,
// v.ModuleName,
// u.FormID,
// t.FormName,
// w.FormName,
t.ParentID,
t.Sequence,
t.IsApprovalRequired,
t.CompanyCategoryID,
t.DocTypeID
//p.CreateBy,
//p.CreateOn,
//p.CreatePc,
//p.UpdateBy,
//p.UpdateOn,
//p.UpdatePc,
//p.IsDeleted,
//p.DeleteBy,
//p.DeleteOn,
//p.DeletePc,
//p.Transfer
};
return query.WhereIf(userID != 0, w => w.UserID == userID).ToList();
}
Put result in session
Session["UserPermission"] = new PermissionGroupUserController().GetSearchUserGroupPermissionData(objEntity.UserID);
Now ,want to get back the record set from session.bellow foreach syntax area as a item contain each row all properties and values but can not assign in a variable just like bellow ,why can not assign an AnonymousType variable value to a variable.
var o = Session["UserPermission"] as IEnumerable; //use casting
foreach (var area in o)
{
//int a = area.UserID;
}
Note:sabove syntax how me error
message:foreach statement cannot operate on variables of type 'object'
because 'object' does not contain a public definition for
'GetEnumerator'
If have any query please ask.
Did you try typecasting oto IEnumerable?
Apart from that, in your foreach loop, you have to use dynamic instead of var. This is required because your type is anonymous.
But i would still strongly suggest you to use normal types instead of Anonumous ones atleast for two reasons
Code reusability.
Better code readability.
I have a small problem in my where clause in the linq expression below. If I put the number 3 instead of department.Id I get the desired result but when I use department.Id I get nothing in the resultset.
I also want to get a count for the number of filters for that filter name using the query again using distinct.
var dept = Page.RouteData.Values["department"];
var department = (from d in db.Departments
where d.Name.Replace(" ", "-") == dept
select new {d.Id, d.Name}).FirstOrDefault();
var query = from p in db.Products
join f in db.ProductFilters on p.Id equals f.ProductId into filters
from x in filters.Where(x => x.Product.DepartmentId == department.Id
/* if == 3 it works */)
select new { x.Name, x.Id };
Promoted to answer from comments:
Have you checked that the department instance is as you think it should be after the first linq statement - ie has an Id == 3?
Your first query is not finding any valid department and is therefore returning default which most probably means that departmend.Id == 0.