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 means that in our data model, the two entities will naturally be related to each other. In this case, if for example, we want to re-run the query first, item description and description of the family, we will not directly instruct the compiler on how the tables are related, but we can refer to the property arranged by EF.
As a result, we can directly query Articles and subsequently select the properties you want in it, knowing that it will find the property Families, which will solve the Join existing between the independent tables, which can be accessed directly from the variable type items.
Code First In this section, we will see a mode of Code-First, usable in the case of this database, leaving for a next article the approach that goes to define the data base to zero or almost. The project that you find in the download section refers to this second mode.
Considering the fact, that the Code-First regardless of whether they come from a predefined template, or will define completely acts with more priority than the basic physical data and the reader, it can then generate it on its own instance of SQL Server. For added convenience, it created a folder named Model, which will contain the classes initially created by EF, but we can make changes to the model. End Using. Following is the GridView containing records. Inserting records to GridView using Entity Framework.
The following event handler is executed when the Add Button is clicked. The name and the country values are fetched from their respective TextBoxes and then passed through an object of Customer class to the AddToCustomers method of Entity Framework. Finally the SaveChanges method of Entity Framework is called which updates the changes to the database and the GridView is again populated with data by making call to the BindGrid method.
AddToCustomers customer ;. SaveChanges ;. AddToCustomers customer. CustomerId which is the primary key is fetched from the DataKey property of GridView while the Name and Country fields are fetched from their respective TextBoxes and are set to the Customer object fetched from the Entity Framework collection using the CustomerId.
Finally the SaveChanges method of Entity Framework is called which updates the changes to the database. ToInt32 GridView1. Values[0] ;. FindControl "txtName" as TextBox. FindControl "txtCountry" as TextBox. FirstOrDefault ;. Rows e. DataKeys e. Values 0. FindControl "txtName" , TextBox. FindControl "txtCountry" , TextBox. Customers Where c.
Select c. Cancel Edit. Here the EditIndex is set to -1 and the GridView is populated with data. If the office location is blank, sets the Instructor. OfficeAssignment property to null so that the related row in the OfficeAssignment table will be deleted. Run the page select the Instructors tab and then click Edit on an instructor. Change the Office Location and click Save. Instructors may teach any number of courses. Now you'll enhance the Instructor Edit page by adding the ability to change course assignments using a group of check boxes.
The relationship between the Course and Instructor entities is many-to-many, which means you do not have direct access to the foreign key properties which are in the join table. Instead, you add and remove entities to and from the Instructor. Courses navigation property. The UI that enables you to change which courses an instructor is assigned to is a group of check boxes.
A check box for every course in the database is displayed, and the ones that the instructor is currently assigned to are selected. The user can select or clear check boxes to change course assignments.
If the number of courses were much greater, you would probably want to use a different method of presenting the data in the view, but you'd use the same method of manipulating navigation properties in order to create or delete relationships.
To provide data to the view for the list of check boxes, you'll use a view model class. Create AssignedCourseData. In InstructorController. The changes are highlighted. The code adds eager loading for the Courses navigation property and calls the new PopulateAssignedCourseData method to provide information for the check box array using the AssignedCourseData view model class.
The code in the PopulateAssignedCourseData method reads through all Course entities in order to load a list of courses using the view model class. For each course, the code checks whether the course exists in the instructor's Courses navigation property.
To create efficient lookup when checking whether a course is assigned to the instructor, the courses assigned to the instructor are put into a HashSet collection. The Assigned property is set to true for courses the instructor is assigned.
The view will use this property to determine which check boxes must be displayed as selected. Finally, the list is passed to the view in a ViewBag property. Next, add the code that's executed when the user clicks Save. Replace the EditPost method with the following code, which calls a new method that updates the Courses navigation property of the Instructor entity.
The method signature is now different from the HttpGet Edit method, so the method name changes from EditPost back to Edit.
Since the view doesn't have a collection of Course entities, the model binder can't automatically update the Courses navigation property. Instead of using the model binder to update the Courses navigation property, you'll do that in the new UpdateInstructorCourses method. Therefore you need to exclude the Courses property from model binding. This doesn't require any change to the code that calls TryUpdateModel because you're using the whitelisting overload and Courses isn't in the include list.
After adding the reference to your Application, you will see App. Config file in Entity Library. From the file, cut the connection string and add this into your Web. Config file. Now, we start coding. Go to your Home controller and open index from view folder, remove everything from index view page.
We will add an anchor link out there to insert the data in the database. Now, we will create an Action to insertData and we will create view for inserting Data. We need form fields to insert the data into the table.
Thus, we will use the model in the view and HTML helper class to create a form. Success using Html. AntiForgeryToken Html.
Firstname Html. Lastname Html. Class Html. Section Html. Rollnumber Html. IsActive Html. You can see that, we have mentioned the same Action Name in the form, but we can't have the same action name with the same parameter, but we can create POST or we can use Method Overloading concept in this.
Add objStudent ; objContext. SaveChanges ; if objStudent.
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