Entity Framework is an open-source object-relational mapper framework for. NET applications supported by Microsoft.
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It eliminates the need for most of the data-access code which is used to interact with the database that developers usually need to write. It provides an abstract level to the developers to work with a relational table and columns by using the domain-specific object. It also reduces the code size of the data specific applications and also the readability of the code increases by using it. This is a new technology for accessing the data for Microsoft application.
The latest version for Entity Framework is 6.
The above figure represents how an entity framework interacts with the domain class and database. It provides a connection between the business entity and data tables in the database. It saves data stored in the properties of business entities and also retrieves data from the database and converts it to business entities objects automatically. Entity Framework will execute the relevant query in the database and then materialize results into instances of your domain objects for you to work within your app. Notice that I expressed the query in native C language constructs and it is not enclosed in quotes.
Had this query contained a syntactic error, the compiler would have caught it at compile time. NET Entity Framework translates this query into the appropriate form for sending to the database. The database evaluates the query and the Object Services layer materializes the results as objects.
So far, all the examples have been read operations. The following code snippet shows how you can create a new RunEvent entity, along with two related Participants:. Simply create a new instance of the RunEvent class and set the properties. In this model, the database server generates the EventID property, so it is not necessary to set it here. After creating the RunEvent object, add it to the list of objects that the object context is tracking by calling the AddToEvents method. The generated object context class has methods for adding objects to each entity set, named AddTo[EntitySetName].
By calling AddToEvents , you make the object context aware of the new Event entity for the purposes of change tracking and communicating with the database. In addition to creating the RunEvent object, the code also creates two Participant objects in much the same way. One of the participants is a volunteer, so it creates an instance of the Volunteer derived class. Finally, the code adds the participant objects to the Participants collection on the RunEvent object.
This establishes the relationship between the event and the participants. At this point the new objects and their relationships only exist in memory. To persist them, you call the SaveChanges method on the context.
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This method propagates all changes it has tracked to the database. In this example, the operations add rows to the tables that store information about events and participants, as well as the link table used to relate the two. Though this example just showed inserting new objects, you can perform updates and deletes in much the same way.
For updates, the code simply modifies the properties of previously read objects. The object context will keep track of the changes and persist them when you call SaveChanges. For deleting entities, the object context provides a DeleteObject method, which you can use to mark an object as deleted. NET Entity Framework propagates the delete operation to the database.
You use a connection object to establish a connection to a model, a command object to specify a query, and a data reader object to retrieve query results. EntityClient represents the results as data records, shaped according to the Entity Data Model. There is no LINQ support at this layer because there are no strongly-typed objects over which queries could be expressed. Also, EntityClient does not support write operations.
To perform inserts, updates, or deletes, you must use the Object Services layer.
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Despite these restrictions, EntityClient is a remarkably useful and efficient way to program against entities. This section looks at some code examples that illustrate EntityClient features. The first line creates a new EntityConnection within a using block this ensures the connection is disposed properly. The EntityConnection constructor takes a connection string. Alternatively, you could have specified any other connection string, as long as it consisted of the three parts described earlier.
After creating the connection object, the code calls the Open method to open the connection. Then it sets the command text to an Entity SQL string. Finally, it calls ExecuteReader to execute the query and obtain a data reader to iterate over the results. This part of the code should look identical to results processing code you may have written against ADO. It uses a while loop to read each record and prints the value of one of its fields. EntityClient uses the same mapping engine as the rest of the ADO. NET Entity Framework for performing query translation.
The engine translates the query written here into database terms and reassembles the results into the shapes specified by the Entity Data Model. Because EntityClient does not materialize objects for the results, the overhead incurred is lower than in the Object Services layer. While the results that come back from EntityClient queries may appear similar to those returned by other data providers, there is one important difference: EntityClient records come with rich metadata that describes the entity types that define the record structure.
You can use this to your advantage when writing code that processes the result data.
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If you wanted to build a more dynamic system that printed all result fields without knowing them in advance, you could use metadata to do so, as the following example shows:. The code in this snippet could go in place of the results processing code in the previous snippet. Within the while loop used to iterate over the result records, you cast the reader to the IExtendedDataRecord interface.
This is a new interface, introduced in the ADO. NET Entity Framework, and provides access to the metadata associated with the results. You can obtain the values by indexing into the data record using the member name. The if-statement that checks whether the member is of type EdmProperty is necessary to filter out navigation properties, which do not appear in the result records. In a real application you could use the metadata returned with EntityClient records to build dynamic UI or to provide more context for the meaning of the results.
Though I did not show it in this article, the same metadata is also available at the Object Services layer. This article provides just a brief overview of the features in the ADO. You do this via query-builder methods that correspond to the various query operators. It composes this predicate with the original query to form a new, more restrictive query.
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Pablo works in the SQL Server product group at Microsoft, designing the future versions of the programming models for working with data. He has been involved in several releases of large scale projects at Microsoft such as SQL Server and the. NET Framework. Before joining Microsoft, Pablo spent some time running a start-up focused on advanced application frameworks development, and before that he split his time between building collaborative applications and creating infrastructure for inference system creation and distributed execution used in risk analysis applications. Prior to moving to the US he resided in the small state of Tasmania in Australia.
Outside of technology Rowan's passions include snowboarding, mountain biking, horse riding, rock climbing and pretty much anything else that involves being active. The primary focus of his life, however, is to follow Jesus.
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