Building ASP.NET Core Web Application With Dependency Injection Passing Objects Between Layers

(5) Repository Layer

Repository layer includes the data access and a generic repository that can retrieve data from a database and map data to a business entity.

When you need to change some columns in tables in a Database, placing all of your database logic in a separate repository layer has less impact on your application.

The code below shows Repository class with Dependency Injection, in this case, Constructor Injection.

After DbContext class is instantiated, each method uses LINQ to retrieve data from database.

public class DeptHistoryRepository: IDeptHistoryRepository {
    private readonly deptempContext _context;
    public DeptHistoryRepository(deptempContext context) {
        _context = context;
    }
    //Get all departments
    public IEnumerable < Department > GetAllDepartment() {
        return _context.Department.ToList();
    }
    //Get Departments by Id
    public Department GetDeptById(short deptId) {
        var deptData = _context.Department.Where(d => d.DepartmentID == deptId).FirstOrDefault();
        return deptData;
    }
    public IEnumerable < EmployeeDepartmentHistory > GetEmpDeptById(short deptId) {
        var list = _context.EmployeeDepartmentHistory.Where(d => d.DepartmentID == deptId).ToList();
        return list;
    }
    //from Person.Person table, (int BusinessEtityID )
    public Person GetPersonById(int Id) {
        Person prn = _context.Person.Where(p => p.BusinessEntityID == Id).FirstOrDefault();
        return prn;
    }
    //from Person.EmailAddress table (int BusinessEtityID)
    public PersonEmailAddress GetEmailById(int Id) {
        PersonEmailAddress EAddress = _context.EmailAddress.Where(e => e.BusinessEntityID == Id).FirstOrDefault();
        return EAddress;
    }
}

(6) Service Layer

A service layer is an additional layer that contains business logic and validation logic.

However, this application does not have complete CRUD operation, only Read operation, the validation logic is not included.

Here is an example of Service class.

public class DeptHistoryRepository: IDeptHistoryRepository {
    private readonly deptempContext _context;
    public DeptHistoryRepository(deptempContext context) {
        _context = context;
    }
    //Get all department
    public IEnumerable < Department > GetAllDepartment() {
        return _context.Department.ToList();
    }
    //Get Department by Id
    public Department GetDeptById(short deptId) {
        var deptData = _context.Department.Where(d => d.DepartmentID == deptId).FirstOrDefault();
        return deptData;
    }
    public IEnumerable < EmployeeDepartmentHistory > GetEmpDeptById(short deptId) {
        var list = _context.EmployeeDepartmentHistory.Where(d => d.DepartmentID == deptId).ToList();
        return list;
    }
    //from Person.Person table, (int BusinessEtityID )
    public Person GetPersonById(int Id) {
        Person prn = _context.Person.Where(p => p.BusinessEntityID == Id).FirstOrDefault();
        return prn;
    }
    //from Person.EmailAddress table (int BusinessEtityID)
    public PersonEmailAddress GetEmailById(int Id) {
        PersonEmailAddress EAddress = _context.EmailAddress.Where(e => e.BusinessEntityID == Id).FirstOrDefault();
        return EAddress;
    }
  }
}

(7) Controller

As mentioned earlier, putting all database logic and business logic into a controller is not a good idea over time.

The Controller talks to the Service layer and the Service layer talks to the Repository layer and each one uses Constructor Injection for DI.

If there are any changes in business logics or databases, this approach is much easier to change the implementation without modifying the controller.

The code below, DeptHistoryController injects the DeptHistoryService and accesses it in Index action.

public class DeptHistoryController: Controller {
    private readonly IDeptHistoryService _srv;
    public DeptHistoryController(IDeptHistoryService srv) {
        _srv = srv;
    }
    public IActionResult Index() {
        var list = _srv.GetAllDepartment();
        return View(list);
    }
    //Department Partial View
    public IActionResult prvShow_subDept(string sId) {
        if (String.IsNullOrEmpty(sId)) {
            return PartialView("_PersonInDept");
        }
        short shortId = short.Parse(sId);
        //Get Dept Name from service
        var deptInfo = _srv.GetDeptById(shortId);
        //Pass Department name to PartialView(PersonInDept)
        ViewBag.vbDeptName = deptInfo.Name;
        //Get persons from EmployeeDepartmentHistory table
        var personsInfo = _srv.GetPersonsFromEmpDeptHistory(shortId);
        return PartialView("_PersonInDept", personsInfo);
    }
    //Personal Detail Pertial View
    public IActionResult prvShow_subPersonDetail(string sId) {
        if (string.IsNullOrEmpty(sId)) {
            return PartialView("_PersonDetail");
        }
        int iId = int.Parse(sId);
        vmPersonDetail personInfo = _srv.GetPersonDetail(iId);
        return PartialView("_PersonDetail", personInfo);
    }
}

(8) Views

In the Model-View-Controller (MVC) design pattern, the view handles data presentation and user interaction. It is like a Presentation Layer.

Below is the Index.cshtml. Because of using Partial Views that reduce the duplication of common markup content, this index page is easier to maintain.

<div id="mainDept" class="Box1">
    <h5 style="text-decoration:underline double;">Department List</h5>
    <div class="index_mainDev">
        <table id="deptTable" border="1">
            <tr class="tblHeader">
                <td>ID</td> <td>Department Name</td> <td>Click to Detail</td>
            </tr>
            @foreach (var item in Model){
                <tr>
                    <td>@Html.DisplayFor(modelItem => item.DepartmentID)</td>
                    <td>@Html.DisplayFor(modelItem => item.Name)</td>
                    <td><input type="button" class="btnDeptIdSelect" value="....." /></td>
                </tr>
            }
        </table>
    </div>
</div>
<div id="subDept" class="Box2">
    <h3>Person in Department</h3>
</div>
<div id="subPerson" class="Box3">
    <h3>Person Details</h3>
</div>

(9) jQuery

jQuery AJAX method updates parts of a Web page without reloading the whole page.

The code below shows that jQuery Ajax method calls Controller/Action Method, in this case, url: '/DeptHistory/prvShow_subDept' , to open Partial View.

function open_subDept(selectedId) {
    $.ajax({
        url: '/DeptHistory/prvShow_subDept',
        type: 'GET',
        data: {
            sId: selectedId
        },
        success: function(result) {
            $("#subDept").empty().append(result);
            $("#subDept").show();
        },
        error: function() {
            alert("There is something wrong!");
        }
    });
}

Conclusion

This application is a large-scale web application and solves the issues of tight coupling and separation of concerns so that the application will be testable, maintainable, and dependable as most developers’ dream.