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;}
}
}
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>();
}
}
Given the following class
public class Model
{
public int ActualInt{get;set;}
public int ComputedInt {get {return ActualInt * 2;}}
}
How would EF not map the ComputedInt.
I also would prefer not suly my domain model with NotMappedAttribute
Fluent is also a pain because I have to keep removing the mapping per context, per computed property and there are a lof of those in the domain model.
Is there a way to do this, simply by convention instead of configuring explicitly?
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();
}
}
}
I have a stored procedure in my Entity Framework Model. I've added a Function Import and mapped the results to a Complex Type.
I want to add an extra property to this Complex type, that I'll populate in my Domain Service, not coming back from the stored procedure. I added a myClass.shared.cs file and implemented added the property like so:
//myClass.shared.cs
public partial class myClass
{
public string myProperty {get;set;}
}
I populate this in my domain service when I return the object, e.g.:
public myClass GetMyClass(int myClassID)
{
myClass theClass= this.ObjectContext.StoredProc(myClassID).FirstOrDefault();
class.myProperty = 12345;
return theClass;
}
When I get the return values of this method on the client side theClass.myProperty is always null but all values from the stored procedure are populated, am I missing something?
I've tried decorating the myProperty with the [DataMember] attribute but this throws the error:
"The type 'myClass' already contains a
definition for 'myProperty'"
How can I get this to return the value set in the Domain Service to the client?
There was no need to put this in the shared.cs class. The shared.cs class copies the actual code over to the client side and is useful for adding methods etc. but to add a new property, all I had to do was add a partial class (NOT in myClass.shared.cs) and decorate it with DataMember.
public partial class myClass
{
[DataMember]
public string myProperty {get;set;}
}
I have a class Address Generated by entity Framework.
I Have an propertie AddressID in this class.
I Would like to be able to add some treatement for this prop in the set process.
EX :
public partial class Address
{
public bool _AddressID;
public bool AddressID{get return AddressID;}
set{
if(value == -1) _AddressID = null;
}
}
Thanks
Of course you can't redefine your AddressID in order to put your custom logic in its setter, as you'll get compiler error:
The type Address already contains a definition for 'AddressID'
But no worries, if you take a look at the EF generated code for your EntityObject (let's assume its name is Address) you'll see that every scalar property of generated Address class has its own version of OnPropertyChanging and OnPropertyChanged method. For example, OnAddressIDChanging and OnAddressIDChanged in this case.
As you can see below, there is no default implementation for these two methods, only a declaration. This perfectly provides you the opportunity to execute custom logic
as the property is about to change (PropertyChanging) as well as just after the property
value has changed (PropertyChanged).
// From the designer code for Address class:
partial void OnAddressIDChanging(global::System.Int32 value);
partial void OnAddressIDChanged();
This is how your Entity Model designer code already is look like (hypotetically):
public global::System.Int32 AddressID {
get {
return _AddressID;
}
set {
if (_AddressID != value) {
// OnPropertyChanging method get called here:
OnAddressIDChanging(value);
ReportPropertyChanging("AddressID");
_AddressID = StructuralObject.SetValidValue(value);
ReportPropertyChanged("AddressID");
// OnPropertyChanged get called here:
OnAddressIDChanged();
}
}
}
So all you need to do in order to hook up your custom code is:
public partial class Address {
partial void OnAddressIDChanged() {
if(AddressID == -1) {
AddressID = 0;
}
}
}
By the way, about other posted answers - with all due respect to them - if you want this solution for a production application then you cannot use "Code First" since it merely is a CTP as for now and will be part of the next release for EF, so it cannot be an option.
About customizing default code generation, while this is indeed possible since in VS 2010, Entity Framework itself also uses T4 for designer code generation and we can take advantage of it by changing the T4, But it is an option only if you want to fundamentally change how the entity classes are generated in general and you cannot use it for customizing a setter logic for a specific entity.
Code First in EF4 is an option - it allows you to fully control all of the code. However, another option is to customize the EF4 T4 templates that ship with EF4. If you have certain patterns in your code that you consistently use, this would be a good approach. You can read more about how to customize the templates here: Customizing Entity Classes in VS2010