I try to read C# ECMA to find out what an entity is but failed.
Is this a instance of class?
Or types+members?
Or any single word in the code that shows no red wavy line under it?
Entity is a semantic i.e. relating to meaning in language or logic. An entity is something that exists in itself, actually or potentially, concretely or abstractly, physically or not. It needs not be of material existence.
An entity usually refers to something, anything really, that has a unique and separate existence.
In software development this word is almost only used to denote that one instance is different from another instance and they are independent of each other.
A class, on the other hand, defines or contains the definition of an object. Once that object is constructed based on the definition, then you get your instance or object instance.
Hope it helps ;)
In C# term entity is commonly related to database representation of the table and should contain an Id attribute.
Generally, an entity is a unit of existence, an existing or real thing. Something that can have properties ascribed to it that distinguishes it from another unit with similar characteristics.
I have a table and you have a table. If I describe my table in enough detail then at some point it will be possible to distinguish my table from yours.
In object-oriented programming an entity corresponds to an object instance. In data modelling it corresponds to a unit of data rather than something necessarily having a physical presence.
I think they are using it in it's broadest meaning
Entity: something having real or distinct existence; a thing, esp when considered as independent of other things
So an Entity can be instance of class and types+members
Depending on the context.
Lets say you are talking about class definitions if two classes can be "considered as independent"(having different namespaces) they will call it an Entity.
If you are talking about some sort of business logic you might use the "Entity" word for all objects that have the same Id value stored in the in memory property or Database.
Essentially if you can have a function areTheSame(x,y)=>[true,false] and the result of the function for all posible x and y can be false you can call that x or y an entity.
An entity in a broader setting is just a "something" that exists.
In the C# ECMA an entity is a placeholder for something that you refer to.
This could be a an instance if you refer to an entity created from a class. Or for example the following section defined a scope the following way:
The scope of a name is the region of program text within which it is possible to refer to the entity declared by the name without qualification of the name.
So to acces a given something (an entity), you need to reference the scope to refer to it. This could be a class, an instance, a static method or else.
Practically speaking and within the realm of CRUD web applications, an entity is simply a class representation of a database table.
Suppose you have a web application consisting of a database with three tables, each having a number of attributes:
Table 1: User
Name
Surname
ID_Number
Table 2: Address
Residential_address
Postal address
Table 3: Preferences
Food
Color
If you wanted to use this database within your web application, you would need to create three entities which look like this.
public class User
{
public string Name { get; set; }
public string Surname { get; set; }
public string IDNumber { get; set; }
}
public class Address
{
public string ResidentialAddress{ get; set; }
public string PostalAddress{ get; set; }
}
public class Preferences
{
public string Food{ get; set; }
public string Color{ get; set; }
}
In a large number of C# web projects, if you deal with databases, your project would likely have a folder called "entities" and it would include classes called entities, just like the examples shown above.
There is quite a bit of qualifying required on the above and it also strongly depends on what framework you use, but the above is the most common practical interpretation on entity.
I am trying to write a model for use within EF6 which includes a property that I would like to calculate in C# (not SQL). My model looks like this:
public class UploadRequestWorkingHours : UploadRequest
{
[DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public int WorkingHoursSinceResponseDate
{
get { return DateUtils.WorkingHoursSince(ResponseDate); }
private set { }
}
}
The UploadRequest class contains the details, and this derived class introduces a property that should be calculated by LINQ/EF/whomever when the model is serialized.
Unfortunately, this property — WorkingHoursSinceResponseDate — is making it into the database, even though I have marked the class as Computed. I have also tried None. I understand from reading the EF documentation that this DatabaseGeneratedOption will still create a column in the database; I have been following posts such as this one that have lots of votes, but in reality, I don't think this is the solution.
How to I prevent a computed property in the model from making it into the DB? Another post suggests creating the migration and commenting out the field in the migration file created but this is very smelly and there's no way I'd get away with this!
Found it: [NotMapped]
Thanks anyway!
I am currently attempting to implement a revision history screen in an MVC app. I need to be able to retrieve the names of fields which have changed in each revision using Envers. So I am following directions here: http://envers.bitbucket.org/#envers-tracking-modified-entities-revchanges
I am using the second option since we have a custom revision entity. It looks like this:
[RevisionEntity(typeof(MyRevisionListener))]
public class RevisionEntity : DefaultTrackingModifiedEntitiesRevisionEntity
{
public virtual Person User { get; set; }
}
As you can see I am inheriting from DefaultTrackingModifiedEntitiesRevisionEntity in order to make sure the class has the property to hold the modified entities' names.
Per the documentation this should create a table called RevChanges in which this information is stored with reference to the revisions table:
Envers provides a simple mechanism that creates REVCHANGES table which
stores entity names of modified persistent objects. Single record
encapsulates the revision identifier (foreign key to REVINFO table)
and a string value.
I am never seeing this table created. I tried creating such a table myself along with a related class and wiring up the mappings, but I don't see how Envers would know to put the data into that table without me configuring it somehow. I just get an exception saying that the object is different from the target type when the get method is called on the new type.
How can I get this to work?
If you use a custom revision entity, you need to map this just like you do with normal entites.
http://envers.bitbucket.org/#revisionlog
I have used Entity Framework and it generated some entity classes for me I want to add a property to one of them there are a lot fields and attribute inside it, when I am going to add property to entity class I have to make child class which is inherited from my entity class then I am usually write this and it works :
IList<newEntity> chid = (from m in db.Entity
select new newEntity
{
//rewrite all properties here
newAttribute = ConvertDate(n.date) //it is example I break it into steps and called some functions to fill new attribute
}).ToList();
My question is how I can avoid rewriting all attribute here it really make me bored to write some code I can just add a new property how I can do that?
I'm not sure if I understood your question correctly, but usually the classes generated by the Entity Framework are partial classes(*), so you don't need to derive from them to add a property. You can add properties, methods etc by adding a class to your codebase with the same name and in the same namespace and then the two definitions are merged by the compiler:
partial class Entity
{
public DateTime newAttribute { get; set; }
}
(*) depending on your code generator
folks, i am new to C# DataEntity Framework.
I have 2 tables in DB :
Vehicle with fields id, measurementId.
Measurement with fields Id, Name.
They related as one to one. One vehicle have one measure.
I want to expand entity Vehicles where i want to store MeasurementName field. I've created property MeasurementName, but how i can bind it to Measurement.Name. Is it possible in DataEntity framework ?
I know that i can achive it another way, for example using Entity Linq where i will create new
class Test
{
Id= id,
Measurement = measurement.Name
};
But is it possible to expand DataEntity to have this property ?
Each of the entities in your model is implemented as a partial class, meaning the total code that defines the class can exist in multiple files but gets compiled into one object. This makes them highly extensible as you can add properties and functions to the code generated by the Entity Framework designer. Create a new partial class with the same name as your entity in the same namespace and add the custom property like so
public partial class Vehicles
{
public string MeasurementName {
get {
return this.Measurement.Name;
}
set {
this.Measurement.Name = value;
}
}
}
If this answer was helpful to you, please be certain to vote it up or mark it as the accepted answer.