Ok, I am trying to find get all subcategories from my database (using query result shaping) that belong to the category that I supply. My class SubCategory includes a List<> of Categories.
The problem is that in the linq statement, g is referring to SubCategory (which in the end contains Categories<>). So the statement below is not allowed.
How do I change the Linq statement to generate the correct SQL query to include all SubCategories that contain the matching Category.
public class SubCategory
{
public int SubCategoryId { get; set; }
public string Name { get; set; }
public string Description { get; set; }
public List<Article> Articles { get; set; }
public List<Category> Categories { get; set; }
}
//incorrect code below:
var SubCategories = storeDB.SubCategories.Include("Categories").Single(g => g.Name == category);
This worked for me (maybe too simple):
var Category = storeDB.Categories.Include("SubCategories").Single(c => c.Name == category);
return Category.SubCategories;
I find it a bit confusing that each SubCategory can belong to more than one Category - have you got this relationship the right way around?
Regardless, I think its probably more readable if you change the select to work on Categories first - i.e. something like:
var subCatQuery = from cat in storeDB.Categories
where cat.Name == category
select cat.SubCategories;
which you can then execute to get your IEnumerable<>:
var subCategories = subCatQuery.ToList();
I find that much more readable/understandable.
(I also find the query syntax easier to read here than the fluent style)
my preferred answer would be to use a linq join. if there aren't but 2 data sets you can use the linq operations .join and .groupjoin vs a from statement. this would be my approach.
Dictionary<MainQuery, List<subQuery>> Query =
dbStore.List<MainQuery>.include("IncludeAllObjects")
.groupjoin(db.List<SubTable>.Include("moreSubQueryTables"),
mainQueryA=>mainQueryA.PropToJoinOn,
subQueryB => sunQueryB.PropToJoinOn,
((main, sub)=> new {main, sub})
.ToDictionary(x=>x.main, x=>x.sub.ToList());
Related
I have a controller that is building a query from Linq to Sql to pass into the ViewBag.products object. The problem is, I cannot loop using a foreach on it as I expected I could.
Here's the code in the controller building the query, with the .ToList() function applied.
var products = from bundles in db.Bundle
join bProducts in db.BundleProducts on bundles.bundleId equals bProducts.bundleID
join product in db.Products on bProducts.productID equals product.productID
join images in db.Images on product.productID equals images.productID
where bundles.bundleInactiveDate > DateTime.Now
select new {
product.productName,
product.productExcerpt,
images.imageID,
images.imageURL
};
ViewBag.products = products.ToList();
Since I am using a different model on the Index.cshtml for other items needed, I thought a simple Html.Partial could be used to include the viewbag loop. I have tried it with the same result with and without using the partial and simply by using the foreach in the index.cshtml. A snippet that includes the partial is below:
<div id="bundle_products">
<!--build out individual product icons/descriptions here--->
#Html.Partial("_homeBundle")
</div>
In my _homeBundle.cshtml file I have the following:
#foreach (var item in ViewBag.products)
{
#item
}
I am getting the ViewBag data, but I am getting the entire list as output as such:
{ productName = Awesomenes Game, productExcerpt = <b>Awesome game dude!</b>, imageID = 13, imageURL = HotWallpapers.me - 008.jpg }{ productName = RPG Strategy Game, productExcerpt = <i>Test product excerpt</i>, imageID = 14, imageURL = HotWallpapers.me - 014.jpg }
What I thought I could do was:
#foreach(var item in ViewBag.Products)
{
#item.productName
}
As you can see, in the output, productName = Awesomenes Game. However, I get the error 'object' does not contain a definition for 'productName' when I attempt this.
How can I output each "field" so to say individually in my loop so I can apply the proper HTML tags and styling necessary for my page?
Do I need to make a whole new ViewModel to do this, and then create a display template as referenced here: 'object' does not contain a definition for 'X'
Or can I do what I am attempting here?
*****UPDATE*****
In my Controller I now have the following:
var bundle = db.Bundle.Where(a => a.bundleInactiveDate > DateTime.Now);
var products = from bundles in db.Bundle
join bProducts in db.BundleProducts on bundles.bundleId equals bProducts.bundleID
join product in db.Products on bProducts.productID equals product.productID
join images in db.Images on product.productID equals images.productID
where bundles.bundleInactiveDate > DateTime.Now
select new {
product.productName,
product.productExcerpt,
images.imageID,
images.imageURL
};
var bundleContainer = new FullBundleModel();
bundleContainer.bundleItems = bundle;
return View(bundleContainer);
I have a model, FullBundleModel
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace JustBundleIt.Models
{
public class FullBundleModel
{
public IQueryable<Bundles> bundleItems { get; set; }
public IQueryable<Images> imageItems { get; set; }
}
}
and my View now has
#model IEnumerable<JustBundleIt.Models.FullBundleModel>
#foreach (var item in Model)
{
<div class="hp_bundle">
<h3>#Html.Display(item.bundleName)</h3>
</div>
}
If I remove IEnumerable from the model reference, the foreach errors out that there is no public definition for an enumerator.
In the #Html.Display(item.bundleName) it errors out that the model has no definition for bundleName. If I attempt
#foreach(var item in Model.bundleItems)
I get an error that bundleItems is not defined in the model.
So what don't I have wired up correctly to use the combined model?
Do I need to make a whole new ViewModel to do this, and then create a
display template as referenced here...
Darin's answer that you linked states the important concept: Anonymous types are not intended for use across assembly boundaries and unavailable to Razor. I would add that it's rarely a good idea to expose anonymous objects outside of their immediate context.
Creating a view model specifically for view consumption is almost always the correct approach. View models can be reused across views if you are presenting similar data.
It's not necessary to create a display template, but it can be useful if you want to reuse the display logic. HTML helpers can also fill a similar function of providing reusable display logic.
Having said all of that, it's not impossible to pass an anonymous type to a view, or to read an anonymous type's members. A RouteValueDictionary can take an anonymous type (even across assemblies) and read its properties. Reflection makes it possible to read the members regardless of visibility. While this has its uses, passing data to a View is not one of them.
More reading:
Can I pass an anonymous type to my ASP.NET MVC view?
Dynamic Anonymous type in Razor causes RuntimeBinderException
Why not create a new model that contains all of the data that you need?
Example One:
public class ContainerModel
{
public IQueryable<T> modelOne;
public IQueryable<T> modelTwo;
}
This will allow you to access either of your queries in Razor:
#model SomeNamespace.ContainerModel
#foreach (var item in Model.modelOne)
{
//Do stuff
}
I personally avoid using ViewBag at all and store everything I need in such models because it's NOT dynamic and forces everything to be strongly typed. I also believe that this gives you a clearly defined structure/intent.
And just for clarity's sake:
public ViewResult Index()
{
var queryOne = from p in db.tableOne
select p;
var queryTwo = from p in db.tableTwo
select p;
var containerModel = new ContainerModel();
containerModel.modelOne = queryOne;
containerModel.modelTwo = queryTwo;
return View(containerModel);
}
Example Two:
public class ContainerModel
{
[DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")] //Format: MM/dd/yyyy (Date)
public Nullable<DateTime> startDate { get; set; }
[DisplayFormat(DataFormatString = "{0:MM/dd/yyyy}")] //Format: MM/dd/yyyy (Date)
public Nullable<DateTime> endDate { get; set; }
public SelectList dropdown { get; set; }
public IQueryable<T> modelOne { get; set; }
public IQueryable<T> modelTwo { get; set; }
}
In this case you've stored 3 other items in the model with your 2 queries. You can use the Html helpers to create a Drop Down List in Razor:
#Html.DropDownList("dropdown", Model.dropdown)
And you can use the DisplayFor helper to display your dates as defined in your model with Data Annotations:
#Html.DisplayFor(a => a.startDate)
This is advantageous IMO because it allows you to define all of the data that you want to make use of in your View AND how you plan to format that data in a single place. Your Controller contains all of the business logic, your Model contains all of the data/formatting, and your View is only concerned with the content of your page.
How would I display data from the following database entity in a format that looks like a table:
public class Attendance
{
public int AttendanceID { get; set; }
public int CourseID { get; set; }
public int StudentID { get; set; }
public int AttendanceDay { get; set; }
public bool Present { get; set; }
public virtual Course Course { get; set; }
public virtual Student Student { get; set; }
}
I would want to find all rows in the Attendance db entry that had CourseID == x; So I would use something like:
AttendanceData = Attendance.Where(s => s.CourseID == x); // I think
Then I would need to be able to sort this information in my view to display it in a way that makes sense. I would want to have a data on screen with all of the present/not present values sorted in a table with StudentIDs listed on the left and AttendanceDays listed accross the top.
How would I sort and display this information?
UPDATE:
Using the following code (along with Mvc WebGrid) - I can get a grid of some sort to appear in my view.
Controller:
IEnumerable<Attendance> model = db.Attendance.Where(s => s.CourseID == 4);
return View(model);
View:
#model IEnumerable<MyProject.Models.Attendance>
<div>
#{
var grid = new WebGrid(Model, defaultSort: "Name");
}
#grid.GetHtml()
</div>
However, the grid is not organized in a manner that is useful for my needs.
I want the top of my displayed table to read:
Day 1 | Day 2 | Day 3 | etc until the max value of "Attendance Day" (which is dictated at the creation of a Course that a student signs up for).
I want the left side of the displayed table to read:
Student ID 1
Student ID 5
Student ID 6
Student ID etc . . until all of the students within the data set have been displayed.
I think I need to use something along the lines of this in my controller:
var model = from s in db.Attendance
where s.CourseID == 4
group s.AttendanceDay by s.StudentID into t
select new
{
StudentID = t.Key,
Days = t.OrderBy(x => x)
};
return View(model);
But I need an IEnumerable<> returned to my view using Mvc WebGrid -- I am getting somewhere, just still a little lost along the way. Can I get a nudge in the right direction?
For a fairly typical set of requirements, it sounds like this would be a good candidate for the ASP.NET WebGrid. It's flexible, allows for paging, sorting, formatting, etc. I've used it for a few projects and works just like any of the other HTML helpers that you're probably used to in ASP.NET MVC.
Here's a good starting place.
We are building dynamic search expressions using the Dynamic Linq library. We have run into an issue with how to construct a lamba expression using the dynamic linq library for navigation properties that have a one to many relationship.
We have the following that we are using with a contains statement-
Person.Names.Select(FamilyName).FirstOrDefault()
It works but there are two problems.
It of course only selects the FirstOrDefault() name. We want it to use all the names for each person.
If there are no names for a person the Select throws an exception.
It is not that difficult with a regular query because we can do two from statements, but the lambda expression is more challenging.
Any recommendations would be appreciated.
EDIT-
Additional code information...a non dynamic linq expression would look something like this.
var results = persons.Where(p => p.Names.Select(n => n.FamilyName).FirstOrDefault().Contains("Smith")).ToList();
and the class looks like the following-
public class Person
{
public bool IsActive { get; set;}
public virtual ICollection<Name> Names {get; set;}
}
public class Name
{
public string GivenName { get; set; }
public string FamilyName { get; set; }
public virtual Person Person { get; set;}
}
We hashed it out and made it, but it was quite challenging. Below are the various methods on how we progressed to the final result. Now we just have to rethink how our SearchExpression class is built...but that is another story.
1. Equivalent Query Syntax
var results = from person in persons
from name in person.names
where name.FamilyName.Contains("Smith")
select person;
2. Equivalent Lambda Syntax
var results = persons.SelectMany(person => person.Names)
.Where(name => name.FamilyName.Contains("Smith"))
.Select(personName => personName.Person);
3. Equivalent Lambda Syntax with Dynamic Linq
var results = persons.AsQueryable().SelectMany("Names")
.Where("FamilyName.Contains(#0)", "Smith")
.Select("Person");
Notes - You will have to add a Contains method to the Dynamic Linq library.
EDIT - Alternatively use just a select...much more simple...but it require the Contains method addition as noted above.
var results = persons.AsQueryable().Where("Names.Select(FamilyName)
.Contains(#0", "Smith)
We originally tried this, but ran into the dreaded 'No applicable aggregate method Contains exists.' error. I a round about way we resolved the problem when trying to get the SelectMany working...therefore just went back to the Select method.
I have the following SQL query:
select
p1.[id],
p1.[useraccountid],
p1.[subject],
p1.[message],
p1.[views],
p1.[parentid],
max(
case
when p2.[created] is null then p1.[created]
else p2.[created]
end
) as LastUpdate
from forumposts p1
left join
(
select
id, parentid, created
from
forumposts
) p2 on p2.parentid = p1.id
where
p1.[parentid] is null
group by
p1.[id],
p1.[useraccountid],
p1.[subject],
p1.[message],
p1.[views],
p1.[parentid]
order by LastUpdate desc
Using the following class:
public class ForumPost : PersistedObject
{
public int Views { get; set; }
public string Message { get; set; }
public string Subject { get; set; }
public ForumPost Parent { get; set; }
public UserAccount UserAccount { get; set; }
public IList<ForumPost> Replies { get; set; }
}
How would I replicate such a query in LINQ? I've tried several variations, but I seem unable to get the correct join syntax. Is this simply a case of a query that is too complicated for LINQ? Can it be done using nested queries some how?
The purpose of the query is to find the most recently updated posts i.e. replying to a post would bump it to the top of the list. Replies are defined by the ParentID column, which is self-referencing.
The syntaxt of left join in LINQ is :
(i put it in VB.NET) :
Dim query = From table1 in myTable.AsEnumarable 'Can be a collection of your object
Group join table2 in MyOtherTable.AsEnumerable
On table1.Field(Of Type)("myfield") Equals table2.Field(Of Type)("myfield")
In temp
From table2 in temp.DefaultIsEmpty()
Where table1.Field(Of Type)("Myanotherfield") is Nothing 'exemple
Select New With { .firstField = table1.Field(Of Type)("Myanotherfield")
.secondField = table2.Field(Of Type)("Myanotherfield2")}
Something like that
Ju
I discovered that NHibernate LINQ support doesn't include joins. That, coupled with an apparent inexperience with complex LINQ queries, I resorted to the following work around:
Add a Modified column to the posts table.
On reply, update parent's Modified column to match reply's Created column
Sort by and retrieve the value of the Modified column for post display.
I think it's a pretty clean work around, given the limitations of the code. I dreadfully wanted to avoid having to resort to adding another entity, referencing a view, or using a stored procedure + data table combination for this particular piece of code only. Wanted to keep everything within the entities and use NHibernate only, and this fix allows that to happen with minimal code smell.
Leaving this here to mark as answer later.
I am writing a method that is passed a List<AssetMovements> where AssetMovements looks something like
public class AssetMovements
{
public string Description { get; set; }
public List<DateRange> Movements { get; set; }
}
I want to be able to flatten out these objects into a list of all Movements regardless of Description and am trying to figure out the LINQ query I need to do this. I thought that
from l in list select l.Movements
would do it and return IEnumerable<DateRange> but instead it returns IEnumerable<List<DateRange>> and I'm not really sure how to correct this. Any suggestions?
This one's been asked before. You want the SelectMany() method, which flattens out a list of lists. So:
var movements = list.SelectMany(l => l.Movements);