A database with duplicate records can be very problematic for your application. They may produce inaccurate results, use storage space, and impair the functionality of the application. Due to this, it’s crucial to be able to rapidly and effectively detect and get rid of duplicate records.

Introduction

For .NET developers, Entity Framework is a potent Object-Relational Mapping (ORM) tool. It may assist you with operations like querying, updating, and removing data in a database and enables you to work with databases using strongly-typed.NET objects. This post will concentrate on using Entity Framework to identify and get rid of redundant records in a database.

Understanding Duplicate Records

When two or more rows in a database table have the same values for every column, duplicate entries are created. Multiple things, including data entry errors, software problems, and hardware issues, might result in duplicate records. Duplicate records might make it harder for your application to acquire accurate data from the database, which can lead to issues.

Install Required Software

• NET Core SDK from here
• Visual Studio or Visual Studio Code from here

Setup the Project

Make sure we have a functioning ASP.NET Core project with Entity Framework installed before we begin. You can start a new project in Visual Studio or by using the dotnet new command if you don’t already have one.

Add the Entity Framework Core package to your project once it has been configured. Run the following command in the Package Manager Console to accomplish this:

Install-Package Microsoft.EntityFrameworkCore

Find Duplicate Records Using Entity Framework in Asp.net Core

In Entity Framework, there are numerous methods for locating duplicate records. Below, we’ll look at a few of the more popular techniques.

Sample Data

 List<Employee> Employees = new List<Employee>
        {
         new Employee{ EmpId= 1, FirstName = "Vicky",LastName= "Pointing" },
         new Employee{ EmpId= 2, FirstName = "John",LastName= "Astle" },
         new Employee{ EmpId= 3, FirstName = "Vicky",LastName= "Pointing" },
         new Employee{ EmpId= 4, FirstName = "Fleming",LastName= "Mick" },
         new Employee{ EmpId= 5, FirstName = "Vicky",LastName= "Pointing" },
         new Employee{ EmpId= 6, FirstName = "Jonty",LastName= "M" },
         new Employee{ EmpId= 7, FirstName = "Vicky",LastName= "Pointing" },
         new Employee{ EmpId= 8, FirstName = "Fleming",LastName= "Mick" }
        };

Group By

The GroupBy approach is one way to identify duplicate records. Based on a given key, this method groups the table’s rows and returns the groups as a collection. We can group the rows by the columns we want to check for duplicates in order to discover duplicate records, and then filter the groups that contain more than one row.

   public IActionResult Index()
        {

            var Employee = Employees.GroupBy(d => new { d.FirstName, d.LastName })
                .Where(g => g.Count() > 1).Select(g => new { g.Key.FirstName, g.Key.LastName });

            ViewBag.DupRecord = Employee;

            return View();
        }
    }

According to columns FirstName and LastName, the rows in the Employee table are grouped by this code, which then filters the groups with more than one row. A list of groups with duplicate records is the outcome.

Using Any

The Any approach is an additional technique for locating duplicate entries. If any element in a sequence matches a given criterion, this method returns true. We can use the Any method to see if any rows in a table meet the requirements for duplicate records in order to find duplicate records. Here’s an illustration:

  public IActionResult Index()
        {
 
             var dupemployee = Employees.GroupBy(d => new { d.FirstName, d.LastName })
               .Any(g => g.Count() > 1);                

            

            return View();
        }

The Any method is used to determine whether any groups of rows in the Employee table that are grouped by Columns FirstName and LastName have more than one row. The outcome is a boolean value that denotes if the table contains duplicate records.

Conclusion

In this post, we looked at numerous methods for finding duplicate records in ASP.NET Core using Entity Framework. You can quickly and efficiently detect and eliminate duplicate records in your database by using the methods outlined here. This will help to ensure that your application functions properly and gives accurate data to your users.

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Django Object Relational Mapping(ORM), makes this process easier by allowing you to work with Python classes instead of SQL queries.

Joining two or more tables to extract relevant data is one of the most common tasks when working with a database. We will look into joining tables with Django ORM in this tutorial.

Database Relationships

Before we dig into joining tables, it is essential to understand the different types of relationships that can exist between tables in a database. The three most common types of relationships are.

• One-to-one(1:1)  – Each record in one table is related to one and only one record in another table.
• One-to-many(1:N) – Each record in one table is related to zero, one, or many records in another table.
• Many-to-Many(N: N) – Each record in one table is related to zero, one, or many records in another table and vice versa.

Create Django Join

Create a Project

First, we need to create a project by running the following commands in your terminal or command prompt

Django-admin startproject Joins_ORM

Create an app

A Django project consists of one or more apps. Creating a new app by running the following command in your terminal or command prompt

Python manage.py startapp jointable

Create a Model

from django.db import models

# Create your models here.

class Author(models.Model):
    FirstName = models.CharField(max_length=100)
    LastName = models.CharField(max_length=100)
    MiddleName = models.CharField(max_length=100)

class Books(models.Model):
    title = models.CharField(max_length=200)
    total_page = models.IntegerField()
    auth_id = models.ForeignKey(Author, on_delete=models. CASCADE)
    

Django Join Tables Using ORM

INNER JOIN

from django.shortcuts import render
from .models import Books,Author

# Create your views here.

def jointable(request):
    books = Books.objects.select_related('auth_id').filter(title='A Better World')

    return render(request,'index.html',{'context':books})

LEFT JOIN

def Leftjoin(request):

    books = Books.objects.filter(Q(auth_id__isnull=True)|Q(auth_id__isnull=False))   
    return render(request,'index.html',{'context':books})

RIGHT JOIN

def Rightjoin(request):

    books = Books.objects.select_related('auth_id').all()

    return render(request,'index.html',{'context':books})

See More How to Add Pagination

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