6. Explore features

Summary:

Learn how to use a LINQ statement such as cache, latency, restriction, and isolation.

Personal study notes are for personal review only. The learning Source is linked in the first article.

Content:

1. Delayed iqueryable execution

Iqueryable query = from C inctx. Customers select C;

Such a query syntax does not cause the statement to be executed immediately. It is just a description and corresponds to an SQL statement. The statement is executed only when necessary.

If you perform two foreach operations, the execution of the two SQL statements will be captured:

Iqueryable query = from C inctx. Customers select C;

Foreach (customer C inquery)

Response. Write (C. customerid );

Foreach (customerc in query)

Response. Write (C. contactname );

For such a requirement, we recommend that you first use tolist () and other methods to save the query results first, and then query the set:

Ienumerable <customer> MERs = (from C inctx. Customers select c). tolist ();

Foreach (customer C incustomers)

Response. Write (C. customerid );

Foreach (customer C incustomers)

Response. Write (C. contactname );

2,Dataloadoptions

Dataloadoptions Options = new dataloadoptions ();

Options. loadwith <product> (P => P. order_details );

Options. associatewith <product> (P => P. order_details.where (OD => OD. quantity> 80 ));

CTX. loadoptions = options;

VaR products = from P in CTX. Products select P;

Linqto SQL has restrictions on the use of dataloadoptions. It only supports one-to-many relationship.

Dataloadoptions Options = new dataloadoptions ();

Options. loadwith <customer> (C => C. Orders );

Options. loadwith <order> (O => O. order_details );

CTX. loadoptions = options;

Ienumerable <customer> MERs = CTX. Customers. tolist <customer> ();

For the many-to-one relationship, there is no restriction on the dataloadoptions:

Dataloadoptions Options = new dataloadoptions ();

Options. loadwith <product> (C => C. Category );

Options. loadwith <product> (C => C. order_details );

Options. loadwith <order_detail> (O => O. Order );

CTX. loadoptions = options;

Ienumerable <product> Products = CTX. Products. tolist <product> ();

3. Primary Key Cache

LINQ to SQL caches the queried objects. If a record is queried only based on the primary key

Read from the cache directly:

Customer C1 = CTX. Customers. Single (customer => customer. customerid = "anrecognition ");

C1.contactname = "Zhuye ";

Customer C2 = CTX. Customers. Single (customer => customer. customerid = "anrecognition ");

Response. Write (c2.contactname );

4. datacontext isolation

 

Sometimes we will pass the object to datacontext from the outside and require it to be updated, because different datacontext are relatively independent. Since the new datacontext does not obtain an object, we can only update the data by appending it.

First, add the primary key field of the customer table with the isversion ID:

[Column (storage = "_ customerid", dbtype = "nchar (5) not null", canbenull = false, isprimarykey = true, isversion = true)]

Run the following test code:

Customer c = new customer {customerid = "alfki", contactname = "Zhuye", companyName = "1111 "}; CTX. Customers. Attach (C, true ); CTX. submitchanges ();