Understanding the Issue with Exporting Data to Excel using LINQ in ASP.NET MVC

In this article, we will delve into the problem of exporting data from a database to an Excel file using LINQ (Language Integrated Query) in ASP.NET MVC. We will explore the issues that arise when exporting data with duplicate records and provide a solution to resolve these problems.

Introduction

ASP.NET MVC provides an excellent way to build dynamic web applications, but one of its limitations is the difficulty in exporting complex datasets to Excel files. In this article, we will discuss how to export data from a database to an Excel file using LINQ in ASP.NET MVC, and address the issue of duplicate records.

The Problem with Duplicate Records

The problem arises when trying to export data to an Excel file, where duplicate records are present in the dataset. This can occur due to various reasons such as:

Data inconsistencies: Inconsistent data entries or incorrect data mapping between the database and the model.
Joining multiple tables: When joining multiple tables using LINQ, it may lead to duplicate records if not handled properly.

The Provided Code

The provided code snippet is a part of an ASP.NET MVC application that retrieves data from two tables (ProductionDays and Models) using LINQ. The retrieved data is then joined with another table (Weeks) based on the WeekId column, which leads to duplicate records in the dataset.

Understanding the Model Classes

The provided model class (ExtractionViewModel) has several properties that correspond to columns in the database tables. This helps in mapping the database columns with the model properties for easier data retrieval and manipulation.

public class ExtractionViewModel
{
    public string Year { get; set; }
    public int Week { get; set; }
    [DataType(DataType.Date)]
    public DateTime Day { get; set; }
    // public string VW240 { get; set; }
    // public string VW270 { get; set; }
    public string VW250 { get; set; }
    public string VW270PA { get; set; }
    public string VW2502PA { get; set; }
}

Understanding the LINQ Query

The provided LINQ query retrieves data from three tables: ProductionDays, Models, and Weeks. It joins these tables based on the WeekId column, which leads to duplicate records in the dataset.

var scheduleList = (from p in db.ProductionDays
                    from m in db.Models
                    from mx in db.Models
                    from mt in db.Models
                    from mv in db.Models
                    from wk in db.Weeks
                    join w in db.Weeks on p.WeekId equals w.WeekId
                    orderby w.Year descending, m.Name descending, p.ProductionDate descending, w.WeekNum descending, mt.Name descending, mx.Name descending, mv.Name descending
                    where (mx.InActive == true)
                    && (mt.InActive == false)
                    && (m.InActive == false)
                    && (mv.InActive == false)
                    && (mt.Name == "VW270")
                    && (mx.Name == "VW250")
                    && (m.Name == "VW270PA")
                    && (mv.Name == "VW250/2PA")
                    select new ExtractionViewModel
                    {
                        Year = w.Year,
                        Day = p.ProductionDate,
                        Week = w.WeekNum,
                        VW270 = mt.Name,
                        VW270PA = m.Name,
                        VW250 = mx.Name,
                        VW2502PA = mv.Name
                    }).ToList();

Resolving the Issue

To resolve the issue of duplicate records when exporting data to an Excel file, we need to consider the following steps:

Optimize the LINQ Query: Review and optimize the LINQ query to minimize the number of duplicate records.
Remove Duplicate Records: Use a technique like Distinct or GroupBy to remove duplicate records from the dataset before exporting it to an Excel file.

Resolving the Issue with Distinct and GroupBy

We can use the Distinct method or the GroupBy method to remove duplicate records from the dataset. Here’s how you can do it:

var scheduleList = db.ProductionDays
    .Join(db.Models, pm => pm.ModelId, m => m.ModelId, (pm, m) =>
        new { ProductionDay = pm, Model = m })
    .Join(db.Weeks, w => w.WeekId, wk => wk.WeekId, (w, wk) =>
        new { w.ProductionDay, wk })
    .GroupBy(x => x.ProductionDay.Year)
    .Select(g => g.Select(x => new ExtractionViewModel
    {
        Year = x.ProductionDay.Year,
        Week = x.ProductionDay.WeekNum,
        Day = x.ProductionDay.Date,
        VW270 = x.Model.VW270,
        VW270PA = x.Model.VW270PA,
        VW250 = x.Model.VW250,
        VW2502PA = x.Model.VW2502PA
    }))
    .SelectMany(g => g)
    .ToList();

Resolving the Issue with Distinct

Alternatively, you can use the Distinct method to remove duplicate records from the dataset.

var scheduleList = (from p in db.ProductionDays
                    join m in db.Models on p.ModelId equals m.ModelId
                    join w in db.Weeks on p.WeekId equals w.WeekId
                    orderby p.ProductionDate descending, w.WeekNum descending
                    select new ExtractionViewModel
                    {
                        Year = w.Year,
                        Week = w.WeekNum,
                        Day = p.ProductionDate,
                        VW270 = m.VW270,
                        VW270PA = m.VW270PA,
                        VW250 = m.VW250,
                        VW2502PA = m.VW2502PA
                    })
    .Distinct((x, y) => x.Year + x.Week + x.Day)
    .ToList();

Exporting Data to Excel

To export the data to an Excel file, you can use a library like EPPlus or OfficeOpenXML.

using OfficeOpenXml;

// ...

var v = new GridView();
v.DataSource = scheduleList;
v.DataBind();

Response.ClearContent();
Response.Buffer = true;
Response.AddHeader("content-disposition", "attachment; filename=ExtractionRecords.xls");
Response.ContentType = "application/ms-excel";
Response.Charset = "";

StringWriter objStringWriter = new StringWriter();
HtmlTextWriter htmlTextWriter = new HtmlTextWriter(objStringWriter);
v.RenderControl(htmlTextWriter);

Response.Output.Write(objStringWriter.ToString());
Response.Flush();
Response.End();

Conclusion

Exporting data from a database to an Excel file using LINQ in ASP.NET MVC can be challenging, especially when dealing with duplicate records. By understanding the issues and optimizing the LINQ query, you can resolve these problems and export your data to an Excel file efficiently.

Last modified on 2024-02-06