Using EF Code First and given an Entity that contains a List, how can I eagerly load the entire object graph for that entity:
Example:
public class Foo
{
public int Id { get; set; }
public List<BarBase> Bars { get; set; }
}
public class BarBase
{
public int Id { get; set; }
public string Text { get; set; }
}
public class BarTypeA : BarBase
{
public List<Baz> Bazes { get; set; }
}
public class BarTypeB : BarBase
{
public List<Quux> Quuces { get; set; } { get; set; }
}
If BarBase were not a base class that could contain instances of several different subtypes, I could use
.Include("Bars").Include("Bars.Bazes")
If I try
.Include("BarBase").Include("BarBase.Bazes").Include("BarBase.Quuces")
I get the error
A specified Include path is not valid. The EntityType 'BarBase' does
not declare a navigation property with the name 'Bazes'.
But how do I handle the situation that Bars can contain different concrete types, and I want to eagerly load all of those instances including the List<T> contained in those concrete types?
This is reported problem in EF currently without a solution.
Related
I'm having trouble understanding how to implement a ViewModel in Asp.net MVC, I have the following tables:
Form
ID, Data
Report
ID, FormID, Owner, Category, Status, SubmissionDate
ReportValues
ID, ReportID, Title, Value
I'm looking for a way to display and edit Report and ReportValues in the one ViewModel where ReportValues.ReportID = Report.ID
ReportValues will have multiple entries that relate to a Report.
I have had a look at similiar questions on here and tried following a tutorial ( http://techfunda.com/howto/262/list-data-using-viewmodel ) and coming up empty handed.
If you need any more information let me know and thanks in advance for any replies!
Your View Model is nothing more than a class. You can solve this many ways, but here's an example.
Create your 3 classes like you normally would.
public class Form
{
public int Id { get; set; }
public string Data { get; set; }
}
public class ReportValues
{
public int Id { get; set; }
public int ReportId { get; set; }
public string Title { get; set; }
public string Value { get; set; }
}
public class Report
{
public int Id { get; set; }
public int FormId { get; set; }
public string Owner { get; set; }
public string Category { get; set; }
public string Status { get; set; }
public DateTime SubmissionDate { get; set; }
}
Then, create your ViewModel class to include the three above classes like this.
public class ReportViewModel
{
public Form Form { get; set; }
public ReportValues ReportValues { get; set; }
public Report Report { get; set; }
}
In your view you can access your three classes and their properties as you would in your controller. Model.Form.Id
Depending on your data types, ReportValues will likely be a property of Report, but that's entirely up to your data structure. You will need to populate the classes using whatever method you want (Entity Framework, ADO, etc.) before you can pass them to your view and use them.
I am buys designing the model below:
public class LogModel
{
public class UserActivityLogs
{
[Key]
public int id { get; set; }
//Id of the user
public string userId { get; set; }
//Time of the log
public DateTime time { get; set; }
public LogActions action { get; set; }
}
// Types of actions to log
public class LogActions
{
[Key]
public int id { get; set; }
public string name { get; set; }
public string description { get; set; }
}
}
Now what I would like to know is do I need to add a table in the context for Logactions as well as UserActivityLogs or will EF see that the two tables are linked and create the log action table automatically?
Also have I specified my relationships correctly? What I was aiming for is that I can define multiple types of Logactions and then a userlog will then have a single log action associated to it.
First, don't use nested classes, it's a needless complication. Use namespaces to organize classes.
Second, don't use plural names for classes. One instance of class represents one entity. Also, use CamelCase names for properties.
Third, yes, Entity Framework will be aware of the associations between the two classes and create a database model with two tables and a foreign key.
So this leaves you with:
namespace MyApp.LogModel
{
public class UserActivityLog
{
[Key]
public int Id { get; set; }
public string UserId { get; set; }
public DateTime Time { get; set; }
public LogAction LogAction { get; set; }
}
public class LogAction
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public string Description { get; set; }
}
}
I am new to MVC.
I have a page which display list of categories. The same page also has a text box to search category. What do I need to do in order to use two models in one single page.
namespace MvcWebsite.Models.User
{
public class ListOfCategories
{
public int lngCatId { get; set; }
public Byte intStatus { get; set; }
public string txtTitle { get; set; }
public ListOfCategories()
{
intStatus = 1;
}
}
public class SearchBox
{
public string txtSearch { get; set; }
}
}
Create a model that incorporates both models - this is called a ViewModel
public class UserViewModel
{
public ListOfCategories ListOfCategories { get; set; }
public SearchBox SearchBox { get; set; }
// optional method to load data into the viewmodel
}
Create a ViewModel class which contains all the properties required for view.
what I understand from your question is that you want to use properties of both two models from a single page. If that is then you need to use the concept of ViewModels , which is known for the solution of such situations. You simply need to create another which will be some thing like this :
public class ThirdModel
{
public ListOfCategories ListOfCategories { get; set; } // properties from one model
public SearchBox SearchBox { get; set; } // properties from second model
}
Now you can access properties of both models in a single model.Thanks
I'm trying to create a model that can optionally refer to a parent of the same type, for example:
public class Category
{
public virtual long CategoryID { get; set; }
public virtual Category? ParentCategory { get; set; }
public virtual int UserID { get; set; }
public virtual string Name { get; set; }
}
As you can see there is an optional member called ParentCategory that is optional and refers to a class of type Category (i.e. the same type). As I'm sure you can guess, I'm trying to create a simple Category tree, where the root node(s) will not have a parent.
This results in the following error when the Entity Framework tries to create the database:
"The ForeignKeyAttribute on property 'ParentCategoryID' on type 'MyProject.Models.Category' is not valid. The navigation property 'Category' was not found on the dependent type 'MyProject.Models.Category'. The Name value should be a valid navigation property name."
I also tried this:
public class Category
{
public virtual long CategoryID { get; set; }
[ForeignKey("Category")]
public virtual long? ParentCategoryID { get; set; }
public virtual int UserID { get; set; }
public virtual string Name { get; set; }
}
But again this resulted in the same error.
Is it possible to model this using EF Code First? Its easy to model it int he database if I were to create the database manually.
Thanks in advance
Ben
Your first example wouldn't even compile because T?, a shortcut for Nullable<T> can only be applied to value types.
The following works fine here:
public class Category
{
public virtual long CategoryID { get; set; }
public virtual Category ParentCategory { get; set; }
}
Now, this will use an ugly name by default for the FK, ParentCategory_CategoryID.
This is a way to get a nicer name, plus some flexibility when using it:
public class Category
{
public virtual long CategoryID { get; set; }
[ForeignKey("ParentCategoryID")]
public virtual Category ParentCategory { get; set; }
public virtual long? ParentCategoryID { get; set; }
}
I feel like this should have a simple answer, but I can't find it.
I have 2 POCOs:
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Product
{
public int Id { get; set; }
public int CategoryId { get; set; }
}
Notice that there are no object references on either POCO. With Code-First, how do I make EF4 CTP5 define a relationship between the two database tables?
(I know this is an unusual scenario, but I am exploring what's possible and what's not with Code-First)
No, this is not possible. As you can see below, all of the fluent API methods for setting up associations require specifying the Navigation Property as their parameter.
HasMany<TTargetEntity>(Expression<Func<TEntityType, ICollection<TTargetEntity>>> navigationPropertyExpression)
HasOptional<TTargetEntity>(Expression<Func<TEntityType, TTargetEntity>> navigationPropertyExpression)
HasRequired<TTargetEntity>(Expression<Func<TEntityType, TTargetEntity>> navigationPropertyExpression)
Is there any particular reason you don't want to use object references? It looks very elegant to use them:
public class Category
{
public int Id { get; set; }
public string Name { get; set; }
public virtual ICollection<Product> Products { get; set; }
}
public class Product
{
public int Id { get; set; }
public Category Category { get; set; }
}
And you can still access the Category Id via your product as product.Category.Id.