在没有数据库连接的情况下使用实体框架

Question

I have an application that I tied to a DB for loading and storing data.

However I don't want to require the user to be on the network and have access to the DB. It just can't load or save without a connection.

I would like to instantiate it without a db connection (just use it in memory), but all constructors use the DB. I would prefer not to modify the entity framework generated .cs file in case I need to update it again from the DB I don't want to wipe out my changes.

How can I use the EF model without a connection?

public partial class SimRunnerEntities : ObjectContext
{
    #region Constructors

    /// <summary>
    /// Initializes a new SimRunnerEntities object using the connection string found in the 'SimRunnerEntities' section of the application configuration file.
    /// </summary>
    public SimRunnerEntities() : base("name=SimRunnerEntities", "SimRunnerEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
        OnContextCreated();
    }

    /// <summary>
    /// Initialize a new SimRunnerEntities object.
    /// </summary>
    public SimRunnerEntities(string connectionString) : base(connectionString, "SimRunnerEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
        OnContextCreated();
    }

    /// <summary>
    /// Initialize a new SimRunnerEntities object.
    /// </summary>
    public SimRunnerEntities(EntityConnection connection) : base(connection, "SimRunnerEntities")
    {
        this.ContextOptions.LazyLoadingEnabled = true;
        OnContextCreated();
    }

All SimRunnerEntities constructors use some sort of valid connection

Answer 1

Instantiating DbContext doesn't open connection to the database. DB connection will be opened after first query is made, where you select something or so. So if you are not modifying or reading any data, you are completely safe working without access to your database.

The thing is, that you can't really do anything with EF DbContext without triggering database, except using it's entity classes for some custom purpose.

The other question is: does you application can really work without using a database? And what are you trying to achieve?

Answer 2

Yes, you can do that.

In example, I have a solution which work with that architecture layout:
Project A - Server Side (WCF)
Project B - Class Library which Contain EF model + DB connection
Project C - Client side(WPF)

A reference to B,
A is WCF and hard copy the configuration from B so it can access the database using the DBContext.

C reference to B,
C is WPF project, the entities being filled from A using WCF and already have the goodies like INPC which already auto generated by EF.

The only thing I had to add in the client side is a custom class container which have list of properties of entities type (ie. List Users {get;set;} and etc..)

---

Further explanation according to comment request:

Q: Can you explain a bit more. If your Project B has a DB connection how does this solution work without a DB connection.

A: sure, project B configuration file (app.config) is simply not being used.
I just have it there for archive purpose or for copy paste..
I did copy and paste it to Project A app.config.

Q: In the UI I want to instantiate a data object but fails without the valid connection string because it include a EF item.

A: Regarding the instantiate an object.. simply as if you instantiate any other object:
var entityX = new MyEntity{fill props code here};
It not requires me to use the Dbcontext to do that.

What I believe might be your next question is how to convoy data from WCF to client side - making the entities "trackable"? and for that I created a whole DTO Layer.. however that is beyond of your original question scope :)
Regarding the simple question can you use the Entities without using the dbcontext to manage them the answer is: Yes.