实体框架和业务对象

Question

I have never used the entity framework before and i would like to try some personal projects implementing it to get my feet wet.

I see that entities can be exposed to the presentation layer. But i don't want certain fields exposed, fields like modified dates and created dates and various other database fields.

how could i implement Business objects and just expose the properties i need but still keep the objects serializable?

Also what advantages does this have over LinqToSql?

Answer 1

When you define an entity in the EDMX model you can specify the visibility of each property's setter and getter, so if you don't want the ModifiedDate to be visible in other layers, you can simply specify it as internal.

If your requirements are more complicated like the ModifiedDate should be accessible in the entities assembly and the business logic assembly but not in the UI assembly, then you need to create another object which will be exchanged between the business logic and the UI logic layers.

Answer 2

How Do I Get Started with the Entity Framework?

Getting Started (Entity Framework)

Entity Framework Tutorials

Answer 3

Personally use a wrapper class over entity and expose or shadow what I need.

// instead of below property in your BLL:

private int m_someVariable;

public int SomeVariable
{
    get { return m_someVariable; }
    set { m_someVariable = value; }
}

// You can use the entity object:

private readonly EntityClass _entityObject = new EntityClass();

public int SomeVariable
{
    get { return _entityObject.SomeVariable; }
    set { _entityObject.SomeVariable = value; }
}

// or make it read-only at your BLL

public int SomeVariable
{
    get { return entityObject.SomeVariable; }
    // set { entityObject.SomeVariable = value; }
}

Answer 4

您只需将所需的属性绑定到表示层，这可以通过声明、业务逻辑层（具有自己的对象抽象级别）或您的 ViewModel 来完成。

Answer 5

      // this is your edmx
        Asset5Entities conx = new Asset5Entities();

// consider this is a new object list of Contact that is a table in the database //using entity framework this database table is mapped to an object for u to handle

            List$gt;Contact$lt; s = new List$gt;Contact$lt;();

//using a big of LINQ u can now select or query over any table in ur database and u have // access to the columns in that table example (Email) here

        var result = from q in conx.Contacts select q.Email;

// rather than

        string sqlcommand = "select email from Contacts";
        Contact con = new Contact();
        con.Email= "xxxx@gmail.com";
        con.FirstName="nader";

        //etc etc... 



        conx.Contacts.AddObject(con);

        //rather than   " insert into Contact values ......................"

        //having your queries within ur c# code rather than strings that are not parsed //for errors but on runtime was alot helpful for me