I'm fairly new at MVC and linq and viewmodels in particular. I managed to get a create and index views to work. The "insert" wasn't as hard as the "list".
I have this linq query:
public ActionResult Index()
{
List<BlendElVM> BEVM = new List<BlendElVM>();
var list = (from Blend in db.blends
join BlendEl in db.blendEl on Blend.ID equals BlendEl.ID
select new
{
Blend.ID, Blend.Title, Blend.TransDt, BlendEl.Comment
}).ToList();
foreach (var item in list)
{
BlendElVM o = new BlendElVM(); // ViewModel
o.Comment = item.Comment;
o.Title = item.Title;
o.TransDt = item.TransDt;
o.ID = item.ID;
BEVM.Add(o);
}
return View(BEVM);
}
What I'm not sure about is the "foreach" section. When I'm running in debug, the "list" shows up fine, but if I comment out the "foreach" I get an error - ie not expecting the model. What does the foreach do? It has to do with the database, but I don't understand the where it is using the "o" and setting the columns. I thought it would all be in one linq query. Is it possible to combine the two and eliminate the "foreach"?
var BEVM = (from blend in db.blends
join BlendEl in db.blendEl on Blend.ID equals BlendEl.ID
select new BlendELVM
{
ID = blend.ID,
Title = blend.Title,
TransDT = blend.TransDt,
comment = blendEl.Comment
}).ToList();
I believe that the foreach is needed in order to read every element in the object so in this case you have:
BlendElVM o = new BlendElVM();
So you're creating and object named " o " of the type BlendELVM and this object contains all the attributes that you declared before which are: ID, Title, TransDT, etc
When you put:
foreach (var item in list)
{
BlendElVM o = new BlendElVM(); // ViewModel
o.Comment = item.Comment;
o.Title = item.Title;
o.TransDt = item.TransDt;
o.ID = item.ID;
BEVM.Add(o);
}
You're assigning to the new object o the item that you're reading in the list and in the end adding it to the BVEM list and answering if you can combine them i will say no because at first you're declaring the query and then you're reading the items on the list and assining them to the BEVM list
Related
I have a controller that accepts a list of strings. THese strings essentially are IDs that a user selects on the view. I need to build the model based upon fields from to tables, hence the need for the join. The bellow code will not build as it claims the properties from the joined table do not exist. It only accepts table 1 values. Item.Well_No and Item.Well_Name throw the error. These are included in the "y" table that i joined to "x"..
[HttpPost]
public ActionResult buildSelectionTable(List<string> dta)
{
var a = from x in db._AGREEMENTS
join y in db.WELL_AGMT_XREF on x.AGMT_NUM equals y.AGMT_NUM
where dta.Contains(x.AGMT_NUM)
select x;
List<AgmtModel> model = new List<AgmtModel>();
foreach (var item in a)
{
model.Add(new AgmtModel { Agmt_Name = item.AGMT_NAME, Agmt_Num = item.AGMT_NUM, Agmt_Type = item.AGMT_TYPE_DESCR, Amnt_Status = item.AGMT_STAT_DESCR, Company = item.CO_NAME, DaysToExp = item.DaysToExp, Drs_Url = item.DRS_URL, Effective_Date = item.EFF_DT, Orig_Lessee = item.ORIG_LESSEE, Prop_Status = item.AGMT_PROP_STAT_DESCR, Expiration_Date = item.EXPR_DATE, Acreage = item.LGL_AREA, Extention_Expiration = item.EXTN_EXPR_DT, WellNo = item.WELL_NO, Well_Name = item.WELL_NAME });
}
return PartialView("_SelectionTable", model);
}
You are only selecting x in your query you need to also select y and reference it.
change select x to be select new { x, y}
and then
foreach (var item in a)
{
model.Add(new AgmtModel { Agmt_Name = item.y.AGMT_NAME, Agmt_Num = item.x.AGMT_NUM ... });
}
you need to insert .x or .y before you the field to determine the field names
alternatively you could actually put the constructor directly in the query
so instead of select x
select new AgmtModel { Agmt_Name = y.AGMT_NAME, etc...}
then you can just return PartialView("_SelectionTable", a.ToList())
Some background
I'm wanting to bind a list of objects (my model-view) to a grid. The model-view contains fields for both an specific entity and fields from a joined entity.
I was getting an error when I would try to bind due to the dbContext being out of scope. I realized I needed to use the .Include() method in order to eager load my navigation property. However, I suspect that since I'm using Linq to Entities, that I'm now generating another error:
"Unable to cast the type 'System.Linq.IQueryable1' to type 'System.Data.Objects.ObjectQuery1'. LINQ to Entities only supports casting EDM primitive or enumeration types."
My code is shown below, any ideas of what I need to do here?
Thanks in advance!
public static List<PlanViewModel> GetPlans()
{
using (var context = new RepEntities())
{
var query = (from p in context.Plans
join r in context.RealEstateDetails on p.ReId equals r.ReId
select new PlanViewModel
{
PlanName = p.PlanName,
TargetCompletionDate = p.TargetCompletionDate,
ActualCompletionDate = p.ActualCompletionDate,
Provision = p.Provision,
StatusTypeId = p.StatusTypeId,
StatusCommon = p.StatusCommon,
Building = r.BuildingName,
City = r.City,
Country = r.Country
}).Include("StatusCommon");
return query.ToList();
}
}
You are almost there, just put Include("StatusCommon") right after context.Plans. Because you need to include StatusCommon before the iteration, this way you can set StatusCommon value for every iteration.
public static List<PlanViewModel> GetPlans()
{
using (var context = new RepEntities())
{
var query = (from p in context.Plans.Include("StatusCommon")
join r in context.RealEstateDetails on p.ReId equals r.ReId
select new PlanViewModel
{
PlanName = p.PlanName,
TargetCompletionDate = p.TargetCompletionDate,
ActualCompletionDate = p.ActualCompletionDate,
Provision = p.Provision,
StatusTypeId = p.StatusTypeId,
StatusCommon = p.StatusCommon,
Building = r.BuildingName,
City = r.City,
Country = r.Country
}).toList();
return query;
}
}
I have the following LINQ query to fill up my model.
var blogs = (from b in Context.Blogs
select new BlogTreeView
{
Created = EntityFunctions.TruncateTime(b.Created),
Children = (from ba in Context.Blogs
where EntityFunctions.TruncateTime(ba.Created) == EntityFunctions.TruncateTime(b.Created)
select new BlogTitle
{
ID = ba.ID,
Title = ba.Title
})
}).Distinct();
The problem is that the distinct gives the following error:
"The 'Distinct' operation cannot be applied to the collection ResultType of the specified argument.\r\nParameter name: argument"
I also tried this:
var blogs = (from b in Context.Blogs
select new BlogTreeView
{
Created = EntityFunctions.TruncateTime(b.Created)
}).Distinct();
This gives me only the unique dates like I want.
Then I've tried to add the childrens to the model with the help of a foreach:
foreach (var item in blogs)
{
item.Children = (from ba in Context.Blogs
where
EntityFunctions.TruncateTime(ba.Created) ==
EntityFunctions.TruncateTime(item.Created)
select new BlogTitle
{
ID = ba.ID,
Title = ba.Title
});
}
But then my return value is null for the children list. In my foreach loop the Children list has the values that I want but not in the return field.
What am I doing wrong, and why did the first query gave me that error?
Few days back I put a question regarding mapping two classes Message and MessageStatusHistory using EF. The mapping is going fine but I am facing some problems with the navigation property StatusHistory in class Message that relates it to MessageStatusHistory objects. I am loading the messages for one user only and want to the statuses pertaining to that user only. Like I would want to show if the user has marked message as read/not-read and when. If I use default loading mechanism like following it loads all the history related to the message irrespective of the user:
IDbSet<Message> dbs = _repo.DbSet;
dbs.Include("StatusHistory").Where(x=>x.MessageIdentifier == msgIdentifier);
To filter history for one user only I tried following trick:
IDbSet<Message> dbs = _repo.DbSet;
var q = from m in dbs.Include("StatusHistory")
where m.MessageIdentifier == msgIdentifier
select new Message
{
MessageIdentifier = m.MessageIdentifier,
/*OTHER PROPERTIES*/
StatusHistory = m.StatusHistory
.Where(x => x.UserId == userId).ToList()
};
return q.ToList();//THROWING ERROR ON THIS LINE
I am getting the error:
The entity or complex type 'MyLib.Biz.Message' cannot be constructed in a LINQ
to Entities query.
I have tried by commenting StatusHistory = m.StatusHistory.Where(x => x.UserId == userId).ToList() also but it has not helped.
Please help me in getting Messages with filtered StatusHistory.
EDIT:- above is resolved with this code:
var q = from m in _repository.DBSet.Include("Histories")
where m.MessageIdentifier == id
select new {
m.Id,/*OTHER PROPERTIES*/
Histories = m.Histories.Where(x =>
x.SenderId == userId).ToList()
};
var lst = q.ToList();
return lst.Select(m => new Message{
Id = m.Id, MessageIdentifier = m.MessageIdentifier,
MessageText = m.MessageText, Replies = m.Replies,
ReplyTo = m.ReplyTo, Histories = m.Histories, SenderId =
m.SenderId, SenderName = m.SenderName, CreatedOn = m.CreatedOn
}).ToList();
But if I try to include replies to the message with:
from m in _repository.DBSet.Include("Replies").Include("Histories")
I am getting error on converting query to List with q.ToList() for Histories = m.Histories.Where(x=> x.SenderId == userId).ToList().
About your EDIT part: You cannot use ToList() in a projection, just leave it an IEnumerable<T> and convert to a List<T> when you construct the Message. You also don't need to create two list objects, you can switch from the LINQ to Entities query to LINQ to Objects (the second Select) by using AsEnumerable():
var list = (from m in _repository.DBSet
where m.MessageIdentifier == id
select new {
// ...
Histories = m.Histories.Where(x => x.SenderId == userId)
})
.AsEnumerable() // database query is executed here
.Select(m => new Message {
// ...
Histories = m.Histories.ToList(),
// ...
}).ToList();
return list;
Be aware that Include has no effect when you use a projection with select. You need to make the properties that you want to include part of the projection - as you already did with select new { Histories.....
I am trying to create a multiple choice questionnaire that is table-driven. There is a Question that has child Choices within each question.
When I iterate the listOfQuestions, the first SQL is executed. I thought by "including" Choices that this would prevent a secondary lookup from occuring when I loop though the Choices for the current Question, but it did not.
Why?
var listOfQuestions = (from q in journeyEastContext.Questions.Include("Choices")
orderby q.QuestionId
select new
{
Question = q,
Choices = q.Choices.OrderBy(c => c.Sequence)
});
foreach (var questionGroup in listOfQuestions)
{
Question question = questionGroup.Question;
Literal paragraph = new Literal
{
Text = "<P/>"
};
this.QuestionPanel.Controls.Add(paragraph);
Label QuestionLabel = new Label
{
Text = question.Text
};
this.QuestionPanel.Controls.Add(QuestionLabel);
//var sortedChoices = from choices in question.Choices
// orderby choices.Sequence
// select choices;
foreach (Choice choice in question.Choices)
{
Literal carrageReturn = new Literal
{
Text = "<BR/>"
};
this.QuestionPanel.Controls.Add(carrageReturn);
RadioButton choiceRadioButton = new RadioButton()
{
ID = String.Format("{0},{1}", question.QuestionId, choice.ChoiceId),
Text = choice.Text,
GroupName = question.QuestionId.ToString()
};
this.QuestionPanel.Controls.Add(choiceRadioButton);
}
}
It is because of the projection being part of the query.
select new
{
Question = q,
Choices = q.Choices.OrderBy(c => c.Sequence)
});
There are a few ways to approach the solution to this, the simplest would be
var quesitonsList = (from q in journeyEastContext.Questions.Include("Choices")
orderby q.QuestionId).ToList();
var listOfQuestions = from q in questionsList
Select new
{
Question = q,
Choices = q.Choices.OrderBy(c => c.Sequence)
});
This would tell EF to execute the first query (with the Choices property eagerly loaded) and then let you run through your iteration without having extra queries fired off.
.Include and .Select do not mix because of the type of query being generated in T-SQL. Basically projections use inner select statements and eagerly loaded properties use denormalization and joins to flatten the record set.