Is it possible to add summary properties(no database column) according LINQ from another property(column) in EF generated class from database and this property don't update(delete or remove from class) when update model from database(because this property(cloumn) is not on database)
Yes, it is. Classed generated by Entity Framework as an Entitied are always marked partial. It lets you extend the functionality with your own properties or method.
Let say your entity class is named Post. You can extend it with code like that:
public partial class Post
{
public int Average
{
get
{
return this.Items.Average();
}
}
}
Because it's not a part of designer-generated file it won't be overwritten when it's regenerated. However, there is one requirement to make it work: your custom part of Post class has to be in exactly the same namespace as code generated by EF.
Try using the [NotMapped] attribute on a property in a partial class. This will be ignored by Entity Framework.
public partial class EntityName
{
[NotMapped]
public int CalculatedProperty
{
get
{
return Numbers.Sum();
}
}
}
Related
I am using EF Core 3.0 and have a requirement to change table name dynamically for which I am thinking to create an extensiion method.
Exact requirement:
I have two tables 'Sample' & 'Sample_History' and I want to acheive somthing like this:
To get records from 'Sample' table: DbContext.Samples.ToList();
To get records from 'Sample_History' table: DbContext.Samples.AsHistory().ToList();
Here, i want to dynamically change name of table from 'Sample' to 'Sample_History' using extension method 'AsHistory'. The obvious way is to get the SQL and change it which i want to aviod. Is there some way I can change entity in dbSet itself?
If i understand your requirement correct then you can try this:
public static class DbSetExtensions
{
public static DbSet<SampleHistory> AsHistory(this DbSet<Sample> sample)
{
return sample.GetService<DatabaseContext>().SampleHistory;
}
}
And for make your extension method generic:
public static class DbSetExtensions
{
public static DbSet<T> ToDbSet<T>(DbSet<Sample> dbSet) where T : class
{
return dbSet.GetService<DatabaseContext>().Set<T>();
}
}
Using MVC4 with Entoty Framework CodeFirst I am having problems with the following scenario:
public class Survey
{
public QuestionCollection Questions {get;set;}
}
public class QuestionCollection : List<IQuestion> //Just for MVC
{ }
public class QuestionType1 : IQuestion { ... }
public class QuestionType2 : IQuestion { ... }
Seems straightforward. Now in my controller I want to get the Survey so i have:
DataContext context = new DataContext ();
var survey = context.Surveys.Include(s => s.Questions).SingleOrDefault(s => s.Id == id);
It does compile but runtime it gives me the error:
A specified Include path is not valid. The EntityType 'Survey' does not declare a navigation property with the name 'Questions'.
What am I doing wrong here?
Is there any good tutorial on this topic?
Entity Framework Code First requires that navigation collections be declared as an ICollection<T>. Also, to enable lazy loading of the associations, it should be virtual. This is because, unless otherwise specified, EF will return a proxy object wrapping your declared class. Since your original QuestionCollection property is a concrete implementation, it can't override that in the proxy and enable the navigation. Questions has to be declared as the interface.
Your concerns and requirements in EF are different than in MVC, and they aren't always compatible. If you really, really wanted QuestionCollection, you'll have to map that.
Your Surveys entity should look like this:
public class Survey
{
public virtual ICollection<Question> Questions { get; set; }
}
Also, EF can't implement entity types declared as an interface. This won't work: public virtual ICollection<IQuestion> - your individual question types must all inheirit from a common abstract or concrete instance. They can still implement the interface, but your entity type properties cannot be declared that way.
I would highly recommend going through this series of blog posts on inheritance structures in
EF.
The way you would set up your questions entities would look like this:
// You can still keep the IQuestion interface around for MVC
public abstract class Question : IQuestion
{
// ... properties ...
}
public class QuestionType1 : Question
{
// ... properties ...
}
public class QuestionType2 : Question
{
// ... properties ...
}
public class Survey
{
// Note, collection of Question, not the interface.
public virtual ICollection<Question> Questions { get; set; }
}
Depending on how exactly you want your table structure to look, the base Question class may or may not be abstract. Refer to the above blog posts to see the various options - Table per Type, Table per Hierarchy, Table per Concrete.
Have a look at this link,I think you need to set some auto policies http://forums.asp.net/t/1816051.aspx/1
When I use database first, after creating the edmx file, all the conceptual models have already been generated. But I want to do some special operations on certain fields. For example, there's a field named 'price'; I want the matching property 'Price' to return double of the 'price'. How can I do that? If I modify the getter in the code, every time I update the model from database, all of the modifications go away.
What's the correct way to do this?
What you can do is create a partial class for entity which contains the Price Property and put a getter like this (A property with double price will be meaningful ),
Public partial class YourEntity{
Public float DoublePrice{
get { return Price*2;}
}
}
Or you can create a class inherited from the entity,
Public partial class Entity:YourEntity{
Public override float Price{
get { return base.Price*2;}
}
}
The default constructor in a generated Entity Framework Entities file is like this:
public ProjectEntities() : base("name=ProjectEntities", "ProjectEntities")
{
this.OnContextCreated();
}
I want to change it to:
public ProjectEntities() : base(UtilClass.GetEnvDependantConnectionStringName(), "ProjectEntities")
{
this.OnContextCreated();
}
This is because I want to have a different connection string for all the dev environments and the production environment, and have no chance they are mixed up (which is what my custom method checks).
How do I do that? This code is thrown away every time the designer file is regenerated.
You need to create another file alongside the auto-created ProjectEntities.Designer.cs, say ProjectEntities.cs. In that you use partial to extend the functionality of your entities class like this:
public partial class ProjectEntities : ObjectContext
{
partial void OnContextCreated()
{
this.Connection.ConnectionString = UtilClass.GetEnvDependantConnectionString();
}
}
The file won't then get changed when you regenerate the .Designer.cs file. You'll have to fetch the connection string yourself...
We fixed it by calling our entities ProjectEntitiesPrivate, and what was partial class ProjectEntities before, is now a non partial class ProjectEntities : ProjectEntitiesPrivate, with the constructor I need:
public class ProjectEntities: ProjectEntitiesPrivate
{
public ProjectEntities():base(UtilClass.GetEnvDependantConnectionStringName())
{
}
....
I have problem with EntityFramework querying. Suppose i have two entities: master and child. In child entity i have field (int)SNumber. Now i want query max number from childs:
labelMaxSNumber.text = (_context.Child.Select(s => s.SNumber)).Max();
This works normally on gui, but i want create this in DataModel:
labelMaxSNumber.text = _context.GetMaxSNumber();
I don't know where post this code: in ObjectContext partial class or in EntityObject partial class?
Yes it is possible. Simply create partial class for your context and add method:
public partial class YourContextName
{
public int GetMaxSNumber()
{
return this.Child.Max(c => c.SNumber);
}
}