In essence, we speak about decoupling between our Applications and the logic of data access, which proves to be a major plus. For example: If we need to move - in the context of a single program - to different manufacturers database, it would be required to review the way and the instructions with which we interface the data manager on duty. Entity Framework approaches At present, EF mainly allows two types of approaches related to this use.
The difference between the two approaches is obvious from their name as with Database-First, we find ourselves in a position, where we have to model a pre-existing database and therefore, to derive from it our objects , while in the Code-mode First, we will have to prepare by giving them the properties representing the table fields to determine the structure of the database.
We can say that the two approaches, beyond some instrumental peculiarity, represent a kind of index of priorities compared to those in power in determining the structure of the data, with which the Application will have to do "before the database" from which they derived classes or "before the" code from which a data base model can be textured. Referencing Entity Framework into projects Before you see a couple of examples of the use of EF, you must reference it in our project, i.
Then we will create a new project in Visual Studio, choose the template that is required in the example, as anticipated, will sort C WinForms. Subsequently, save the solution important to avoid alerts being added EF and then we open manage Nuget packages. In it, we will package the entity framework and it will simply add to our solution, using the "Install" button. When finished, we will see how one of the project references have been included to those related to EF.
We are now ready to use the potential of our ORM, as far as development is concerned. We will also see how to carry out an initial database connection and modeling classes, following the two paradigms mentioned above.
Database-First Let us first consider the Database-First mode, which - as we said - is mainly directed to the existing database, i. We recall once again that, at least during the writing of this article, by EF7 onwards, this mode has been suppressed in favor of Code-First and is an important point to keep in mind, when you are going to evaluate the analysis of a solution. Run the script and we will have few records.
Modelling classes with EF Let's see how to model the Visual Studio side, the classes to which we refer in our program to use these data entities. Once you confirm your choice, Visual Studio will launch the Wizard dedicated to Entity Data Model, so that we can indicate what type of model is used. Our choice, in this case, will be "EF Designer from database ', which realizes the Database-First paradigm. You will be asked to make a connection to our database, press "New Connection" and we will subsequently set the connection parameters.
In the following image, an example to adapt to the real development environment is depicted. We will see the generated connection string and we can save it in App. Finally, we will be asked which entities will arise in the model. In our case, we select the two tables created, leaving the rest of the settings as proposed.
The wizard will complete the operations of the event. It is going to generate a data model that consists of the representatives of the classes of the database entities and showing a graphical representation, on which we can act to create such explicit associations between tables, or change some of the mentioned properties. Important Following the Database-First paradigm, we have already mentioned how the database will provide the framework modeling classes and not vice versa.
Therefore, if in this mode we will modify some property and then we will find ourselves in the situation of regenerating the model, these changes - present only on one sideof the code - will be lost, overwritten to that stated on the database. By browsing in the classes the wizard has created for us, we note two of particular interest, namely hierarchically - are daughters of TechnetModello.
Opening them, we will notice that following the structure of the tables to which they refer, exposing the class name as that of the same table and the fields of their counterpart, appropriately converted to the types used in the side code. FirstOrDefault ; MessageBox.
Show art. We perform the Where method on items class, using lambda function that selects the desired item number, returns the first object found by FirstOrDefault method do not operate here validity checks of the data, which of course in a real context must be provided. At this point, using the art variable, we can refer to its properties and then ask for the issuance of a MessageBox text having equal to DESART properties of art, we get the following output: It is evident that the huge potential of the Entity Framework, which for the developer translates into the factors of primary importance, such as the considerable saving of time and being able to dedicate their efforts to the solution itself, rather than to the intermediate layer between it and the database, which is now fully managed.
Relations between tables, and model consequences In the model, we have determined that the two entities Articles and Families were linked together. In fact, we have not defined Foreign Keys that could have instructed EF how to tie the two tables, which are independent. In this condition, we will have to resort to more elaborate LINQ instructions, which implement the joins, that are missing at the model level.
Suppose we want to select the item ART and we want to expose the screen in the product description rather than that of the same class. Join db. Articoli, performing a Join with db.
Famiglie, on the basis of their respective CodFamiglia fields and extracting from that; joins a new object that contains the properties of both. The Where method that accesses the Articles class and makes the selection on Codart field runs on this object, and then returns the first element of the question. Our art variable is now a composite type and we can access respectively to the properties of the part and of the part item's Families: note how in MessageBox there is the description of the article to be emitted, as well as that of the family.
By running a test in the search for the product ART, the displayed result is the following: If we had taken account of this constraint in the design phase, by inserting the Foreign Keys where appropriate, EF would notice it and would be going to create this kind of report automatically. Then we perform a variation on the database structure to see how this affects things in modeling classes.
Once you save the changes to the database, Visual Studio side will have to regenerate the data model. Hence, we will see that our model will be upgraded by establishing a relationship between the two tables. This step is to modify our classes in an important way. This is because most of the new frameworks are building upon the entity framework.
For example WCF data services etc. Why choose Entity Framework:. Read more articles on Entity Framework :. MVC 5. Next Recommended Reading. Windows 10 Vs Windows Visual Studio Vs Visual Studio Understanding Matplotlib With Examples. Understanding Numpy With Examples. C Evolution. Everything That Every. NET applications supported by Microsoft. It enables developers to work with data using objects of domain specific classes without focusing on the underlying database tables and columns where this data is stored.
With the Entity Framework, developers can work at a higher level of abstraction when they deal with data, and can create and maintain data-oriented applications with less code compared with traditional applications. NET developers to work with a database using. NET objects. It eliminates the need for most of the data-access code that developers usually need to write.
As per the above figure, Entity Framework fits between the business entities domain classes and 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.
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