Entity Framework–DB First (DbContext Name)

By default, the name is XXXEntities, suggest to change to XXXContext, because it represents followings:

1. The Connection String in Web.config

2. The Entity Container Name

3. The Class Name of DbContext

 

The Model Namespace, not that important

 

Above 2 names will appear in the property window

 

This shows the name of DbContext class defined before

Building and Inserting Graphs (with Tracked Objects)

A graph tree of our example, Customer is the root

 

Let’s see how to create a customer with order detail data

1. A function, GetProducts() to get existing product setup in the database

2. A function, CreateCustomerWithOrder() to create a Customer and its ContactDetail record

3. Before that, call GetProducts() function to get existing product setup

4. Within the same function, CreateCustomerWithOrder(), new an Order with 2 new LineItem (but using existing product)

5. Add the Order into Customer

6. Add the Customer into context

Following picture shows objects tracked by DbContext

Put breakpoint on using (var context = new SalesOrderDBContext()) to see customer class

1. Customer is there

2. ContactDetail is there

3. Order is there

4. LineItem is there

5. Product is also there, but it’s not what we want

 

The solution to solove it by using Product.ProdictID

This time, no product insert only LineItem

 

By the way, sometimes we will encounter error when Context.SaveChanges(), that is because one or more properties we did not assign them the value.

The error message is DbEntityValidationException was unhandled

 

Additional information:

Disconnected graphs:

DbContext APIs (for Insert, Update, Delete and Get)

The model of SalesOrder.edmx

SalesOrder.Context.cs

SalesOrderDBContext : DbContext

 

GetCustomers()

Context.Entity.ToList()

 

GetCustomer(int id)

Context.Entity.Find(primary_key)

TOP (2): to make sure Find() is always return 1 record, so it will raise an exception if SQL server return 2 records

 

InsertCustomer()

1. Context.Entity.Add(item)

2. Context.SaveChanges()

3. Able to get primary key after insertion

INSERT and SELECT are in a single transaction

1. For context.CustomerSet.Add(customer);

2. For customer.Id

 

UpdateCustomer()

SELECT and UPDATE are in different transactions

Hardcode name for WHERE condition

 

DeleteCustomers()

Context.Entity.Remove(item)

SELECT and DELETE are in different transactions

Entity Framework–Model First, Part 4 (Diagram & Color)

We are able to separate all entities into several diagrams, it is no such limitation to put all in one model design diagram.

First, open Model Browser by VIEW –> Other Windows –> Entity Data Model Browser

Add a new diagram named Product, and add 2 entities Product and Category by follow the steps in this blog

Switch to previous diagram, Diagram1, Add a new Association

In this window, we can also see Product & Category entities even they are not belong to this diagram

After that, we see Product navigation property has been added into Order

Order has been added into Product as well, but different diagram

 

In the meanwhile, we can change the color of entity by changing its Fill Color property to other color

The result will be look like this if we change to red color

 

Let’s see what happen if we Generate Database from Model… again with new add diagram and association in the model

Obviously, the script drop all existing Foreign Key constraints and all existing Tables

Entity Framework–Model First, Part 3 (Execute script to create database)

In previous step(Generate database schema), we successfully generated xxx.edmx.sql script file

 

Look at table definition, we can see what we did changes

1. The Max Length of Industry = 50

2. The Type of OrderDate & ShipToAddress, datetime & geography

The Primary Key constraints

The Foreign Key constraints

 

Now if everything is ok, we can then right-click to Execute the script

Make sure again we are connect to right destination, click Connect button for next step

Once done, we are able to see the successfully completed message

The final step, we can open Server Explorer to check the database and tables are all been created