Blog garden modernization-Prepare to use Entity Framework to update data on demand

Here, "On-Demand Update" refers to updating only the modified data. For example, when we open the casual editing page in the background of a blog, there is a lot of data that can be modified, but we only changed the casual title, and nothing else was changed, the database only updates the title field, which is updated on demand.

Currently, we use a very backward method. A stored procedure with many parameters, No matter what information you modify, even if you only change the title, all fields must be updated when they are saved.

The modernization of the blog Park is not just a slogan. Efforts must be made to change the backward areas.

One feature of Entity Framework showed us hope that it was worthwhile to introduce the modern equipment of Entity Framework.

The Entity Framework can track the changes in object attributes. Only modified attributes are updated when saved to the database. Below we useCodeTake a look at this feature of Entity Framework.

Object Class blogpost:

 Public     Class  Blogpost
{
  Public     Int  Id { Get  ;  Set  ;}
  Public     String  Title {  Get  ;  Set  ;}
  Public     String  Description {  Get ;  Set  ;}
  Public     String  Author {  Get  ;  Set  ;}
} 

Blogdbcontext:

Public ClassBlogdbcontext: dbcontext
{
PublicDbset<Blogpost>Blogposts {Get;Set;}
}
 

Data Update operations:

 Blogpost post  =     New  Blogpost ()
{
ID =     3560  ,
Title  =     "  Title Test  "  ,
Description  =     "  Description Test  "  ,
Author  =    "  Blog  "  
};
  Using  (Blogdbcontext Context  =     New  Blogdbcontext ())
{
Context. blogposts. Attach (post );
Post. Title  =     "  Title changed  " ;
Post. Description  =     "  Description Test  "  ;
Context. savechanges ();
} 

This data update operation only updates the post title (only the title is modified). Let's take a look at the final SQL statement executed by Entity Framework:

ExecSp_executesql n'Update [DBO]. [blog_content]
Set [title] = @ 0
Where ([ID] = @ 1)
', N'@ 0 nvarchar (128), @ 1 int',@ 0=N'Title changed',@ 1=3560
 

Very powerful. Only the title field is updated.

However, there is always a big gap between ideal and reality. To apply this powerful feature to Web applicationsProgramAnd will face many challenges.

Let's take a look at the above data update code: to update the object before attach changes within the context lifecycle, modify the object and save it.

In web application scenarios, you cannot pass object to the client within the context lifecycle and modify the object on the client.

The actual application scenarios we need to deal with are as follows (ASP. net mvc + Ajax ):

1. the client browser first initiates a request to the server. The request obtains a page containing the original attribute value of the object to be modified. The server end is within the lifecycle of the context (blogdbcontext instance, complete a query operation.

2. Modify the property value in the browser of the client.

3. Send all attribute values (modified and unmodified) to the server in JSON format.

4. the server creates a blogpost instance -- modifiedblogpost (if there is no cache, to obtain the blogpost instance by querying the database, and then assign the JSON data to the corresponding attribute ).

5. In the lifecycle of the business logic layer in context (a new blogdbcontext instance:

A) Get the modified blogpost instance originalblogpost (if there is no cache, query from the database );

B) Attach (originalblogpost );

C) Copy all attribute values of modifiedblogpost to originalblogpost;

D) savechanges ();

Problems in this scenario (repeated operations ):

1. Operations on obtaining objects before modification in items 1 and 5..

2. Operations for assigning values to object attributes in item 4th and item 5. c.

Solution:

The JSON data sent from the client is directly transmitted to the business logic layer in the form of strings, and then the originalblogpost attribute assignment operation in the business logic layer based on JSON data is completed directly in 5.C.

This article records a piece of detail in the modernization process of the blog Park. Next, we will overcome this problem and continue to work hard...