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For most of these topics, you'll work with pages that you already created. To use raw SQL to do bulk updates you'll create a new page that updates the number of credits of all courses in the database: You have the following options: SqlQuery method for queries that return entity types. The returned objects must be of the type expected by the DbSet object, and they are automatically tracked by the database context unless you turn tracking off.
See the following section about the AsNoTracking method. SqlQuery method for queries that return types that aren't entities. The returned data isn't tracked by the database context, even if you use this method to retrieve entity types.
ExecuteSqlCommand for non-query commands. One of the advantages of using the Entity Framework is that it avoids tying your code too closely to a particular method of storing data. It does this by generating SQL queries and commands for you, which also frees you from having to write them yourself.
But there are exceptional scenarios when you need to run specific SQL queries that you have manually created, and these methods make it possible for you to handle such exceptions.
As is always true when you execute SQL commands in a web application, you must take precautions to protect your site against SQL injection attacks. One way to do that is to use parameterized queries to make sure that strings submitted by a web page can't be interpreted as SQL commands.
In this tutorial you'll use parameterized queries when integrating user input into a query. To see how this works you'll change the code in the Details method of the Department controller. FindAsync method call with a db.
SqlQuery method call, as shown in the following highlighted code: Calling a Query that Returns Other Types of Objects Earlier you created a student statistics grid for the About page that showed the number of students for each enrollment date.
The code that does this in HomeController. Students group student by student. To do that you need to run a query that returns something other than entity objects, which means you need to use the Database. It displays the same data it did before.
Calling an Update Query Suppose Contoso University administrators want to be able to perform bulk changes in the database, such as changing the number of credits for every course. If the university has a large number of courses, it would be inefficient to retrieve them all as entities and change them individually.
In this section you'll implement a web page that enables the user to specify a factor by which to change the number of credits for all courses, and you'll make the change by executing a SQL UPDATE statement.
The web page will look like the following illustration: RowsAffected variable, and the view displays an empty text box and a submit button, as shown in the preceding illustration. When the Update button is clicked, the HttpPost method is called, and multiplier has the value entered in the text box.
The code then executes the SQL that updates courses and returns the number of affected rows to the view in the ViewBag. When the view gets a value in that variable, it displays the number of rows updated instead of the text box and submit button, as shown in the following illustration: Enter a number in the text box: You see the number of rows affected: Click Back to List to see the list of courses with the revised number of credits.
No-Tracking Queries When a database context retrieves table rows and creates entity objects that represent them, by default it keeps track of whether the entities in memory are in sync with what's in the database.
The data in memory acts as a cache and is used when you update an entity. This caching is often unnecessary in a web application because context instances are typically short-lived a new one is created and disposed for each request and the context that reads an entity is typically disposed before that entity is used again.
You can disable tracking of entity objects in memory by using the AsNoTracking method. Typical scenarios in which you might want to do that include the following: A query retrieves such a large volume of data that turning off tracking might noticeably enhance performance.Writing a thesis or essay?
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These patterns are intended to create an abstraction layer between the data access layer and the business logic layer of an application. Implementing these patterns can help insulate your application from changes in the data store and can facilitate automated unit testing or test-driven development (TDD).
writing additional code to.
The purpose of writing an extended essay is for you to be able to pose insightful questions appropriate to the topic, focus the topic, engage in a systematic research process, develop creative and critical thinking, work independently, develop writing and communication skills, .
Health care clearinghouses, if the only protected health information they create or receive is as a business associate of another covered entity. See 45 CFR (b)(1). A correctional institution that is a covered entity (e.g., that has a covered health care provider component).
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