使用 Dynamic Linq 和 EPPlus 导出到 Excel？

Question

作为一个概述，我正在尝试将Export() 功能添加到我的应用程序中——允许用户指定某些模型字段并仅通过使用LINQ 查询和使用EPPlus 库导出这些字段中的值来导出。我正在尝试基于 THIS 示例在我的 MVC5/EF Code-First 应用程序中实现动态 LINQ 功能，但到目前为止运气不佳。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using InventoryTracker.DAL;
using OfficeOpenXml;
using InventoryTracker.Models;
using System.Linq.Dynamic;


namespace InventoryTracker.Controllers
{
    public class ExportController : Controller
    {
        InventoryTrackerContext _db = new InventoryTrackerContext();
        public static List<DynamicColumns> DynamicColumnsCollection = new List<DynamicColumns>();

        [HttpPost]
        public ActionResult ExportUsingEPPlus(ExportAssetsViewModel model)
        {
            //FileInfo newExcelFile = new FileInfo(output);
            ExcelPackage package = new ExcelPackage();
            var ws = package.Workbook.Worksheets.Add("TestExport");  

            var exportFields = new List<string>();
            foreach(var selectedField in model.SelectedFields)
            {
                // Adds selected fields to [exportFields] List<string>
                exportFields.Add(model.ListOfExportFields.First(s => s.Key == selectedField).Value);
            }

            //int cnt = 0;
            //foreach(var column in exportFields)
            for (int cnt = 0; cnt < 10; cnt++ )
            {
                DynamicColumnsCollection.Add(new DynamicColumns()
                {
                    Id = cnt,

                    ip_address = "ip_address" + cnt,
                    mac_address = "mac_address" + cnt,
                    note = "note" + cnt,
                    owner = "owner" + cnt,
                    cost = "cost" + cnt,
                    po_number = "po_number" + cnt,
                    description = "description" + cnt,
                    invoice_number = "invoice_number" + cnt,
                    serial_number = "serial_number" + cnt,
                    asset_tag_number = "asset_tag_number" + cnt,
                    acquired_date = "acquired_date" + cnt,
                    disposed_date = "disposed_date" + cnt,
                    verified_date = "verified_date" + cnt,
                    created_date = "created_date" + cnt,
                    created_by = "created_by" + cnt,
                    modified_date = "modified_date" + cnt,
                    modified_by = "modified_by" + cnt
                });
            }

            //var selectStatement = DynamicSelectionColumns(exportFields);
            IQueryable collection = DynamicSelectionColumns(new List<string>() {
                "id",
                "owner",
                "note"
            });

            // Loops to insert column headings into Row 1 of Excel
            for (int i = 0; i < exportFields.Count(); i++ )
            {
                ws.Cells[1, i + 1].Value = exportFields[i].ToString();
            }

            // Process data from [collectin] into Excel???
            ws.Cells["A2"].LoadFromCollection(collection.ToString());

            //    ws.Cells["A2"].LoadFromCollection(selectStatement.ToString());

            var memoryStream = new MemoryStream();
            package.SaveAs(memoryStream);

            string fileName = "Exported-InventoryAssets-" + DateTime.Now + ".xlsx";
            string contentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";

            memoryStream.Position = 0;
            return File(memoryStream, contentType, fileName);
        }

        public IQueryable DynamicSelectionColumns(List<string> fieldsForExport)
        {
            using (var db = new InventoryTrackerContext())
            {
                string fieldIds = "," + "4,5,3,2,6,17,11,12" + ",";

                //var taskColum = Enum.GetValues(typeof(EnumTasks)).Cast<EnumTasks>().Where(e => fieldIds.Contains("," + ((int)e).ToString() + ",")).Select(e => e.ToString().Replace("_", ""));
                var taskColum = Enum.GetValues(typeof(EnumTasks)).Cast<EnumTasks>().Where(e => fieldIds.Contains("," + ((int)e).ToString() + ",")).Select(e => e.ToString());

                ////string select = "new (  TaskId, " + (taskColum.Count() > 0 ? string.Join(", ", taskColum) + ", " : "") + "Id )";
                //string select = "new (  " + string.Join(", ", fieldsForExport) + ")";

                ////return db.INV_Assets.ToList().Select(t => new DynamicColumns() { Id = t.Id, TaskId = Project != null ? Project.Alias + "-" + t.Id : t.Id.ToString(), 

                if (!fieldsForExport.Any())
                {
                    return null;
                }

                string select = string.Format("new ( {0} )", string.Join(", ", fieldsForExport.ToArray()));

                var collection = DynamicColumnsCollection.Select(t => new DynamicColumns()
                    {
                        Id = t.Id,
                        //Manufacturer = Convert.ToString(t.Manufacturer.manufacturer_description),
                        //Type = t.Type.type_description,
                        //Location = t.Location.location_room,
                        //Vendor = t.Vendor.vendor_name,
                        //Status = t.Status.status_description,
                        ip_address = t.ip_address,
                        mac_address = t.mac_address,
                        note = t.note,
                        owner = t.owner,
                        cost = t.cost,
                        po_number = t.po_number,
                        description = t.description,
                        invoice_number = t.invoice_number,
                        serial_number = t.serial_number,
                        asset_tag_number = t.asset_tag_number,
                        acquired_date = t.acquired_date,
                        disposed_date = t.disposed_date,
                        verified_date = t.verified_date,
                        created_date = t.created_date,
                        created_by = t.created_by,
                        modified_date = t.modified_date,
                        modified_by = t.modified_by
                    }).ToList().AsQueryable().Select(select);

                return collection;
            }
        }

    }

    public class DynamicColumns : INV_Assets
    {
        public string Model { get; set; }
        public string Manufacturer { get; set; }
        public string Type { get; set; }
        public string Location { get; set; }
        public string Vendor { get; set; }
        public string Status { get; set; }
        public string ip_address { get; set; }
        public string mac_address { get; set; }
        public string note { get; set; }
        public string owner { get; set; }
        public string cost { get; set; }
        public string po_number { get; set; }
        public string description { get; set; }
        public string invoice_number { get; set; }
        public string serial_number { get; set; }
        public string asset_tag_number { get; set; }
        public string acquired_date { get; set; }
        public string disposed_date { get; set; }
        public string verified_date { get; set; }
        public string created_date { get; set; }
        public string created_by { get; set; }
        public string modified_date { get; set; }
        public string modified_by { get; set; }
    }

    public enum EnumTasks
    {
        Model = 1,
        Manufacturer = 2,
        Type = 3,
        Location = 4,
        Vendor = 5,
        Status = 6,
        ip_address = 7,
        mac_address = 8,
        note = 9,
        owner = 10,
        cost = 11,
        po_number = 12,
        description = 13,
        invoice_number = 14,
        serial_number = 15,
        asset_tag_number = 16,
        acquired_date = 17,
        disposed_date = 18,
        verified_date = 19,
        created_date = 20,
        created_by = 21,
        modified_date = 22,
        modified_by = 23
    }





    //https://stackoverflow.com/questions/5796151/export-model-data-to-excel-mvc
    //https://landokal.wordpress.com/2011/04/28/asp-net-mvc-export-to-excel-trick/


}

我的代码正在将我的视图上的 MultiSelectList 中的选定列值导出到 Excel 电子表格的第 1 行，但我的动态 linq 查询有问题，因为获取输出的数据只是值 0在A2:A180 中，无论我为输出指定多少字段。

任何有更多经验或使用过System.Linq.Dynamic 的人都可以对此发表看法吗？

Answer 1

这是我使用了一段时间的东西：

public class ExcelExportHelper
    {
        public static string ExcelContentType { get { return "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"; } }

        public static DataTable ToDataTable<T>(List<T> data)
        {
            PropertyDescriptorCollection props = TypeDescriptor.GetProperties(typeof(T));
            DataTable table = new DataTable();

            for (int i = 0; i < props.Count; i++)
            {
                PropertyDescriptor prop = props[i];
                //table.Columns.Add(prop.Name, prop.PropertyType);
                table.Columns.Add(prop.Name, Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType); // to avoid nullable types
            }

            object[] values = new object[props.Count];
            foreach (T item in data)
            {
                for (int i = 0; i < values.Length; i++)
                {
                    values[i] = props[i].GetValue(item);
                }

                table.Rows.Add(values);
            }
            return table;
        }

        public static byte[] ExportExcel(DataTable dt, string Heading = "", params string[] IgnoredColumns)
        {
            byte[] result = null;
            using (ExcelPackage pck = new ExcelPackage())
            {
                ExcelWorksheet ws = pck.Workbook.Worksheets.Add("Exported Data");
                int StartFromRow = String.IsNullOrEmpty(Heading) ? 1: 3;

                // add the content into the Excel file
                ws.Cells["A" + StartFromRow].LoadFromDataTable(dt, true);

                // autofit width of cells with small content
                int colindex = 1;
                foreach (DataColumn col in dt.Columns)
                {
                    ExcelRange columnCells = ws.Cells[ws.Dimension.Start.Row, colindex, ws.Dimension.End.Row, colindex];
                    int maxLength = columnCells.Max(cell => cell.Value.ToString().Count());
                    if (maxLength < 150)
                        ws.Column(colindex).AutoFit();

                    colindex++;
                }

                // format header - bold, yellow on black
                using (ExcelRange r = ws.Cells[StartFromRow, 1, StartFromRow, dt.Columns.Count])
                { 
                    r.Style.Font.Color.SetColor(System.Drawing.Color.Yellow);
                    r.Style.Font.Bold = true;
                    r.Style.Fill.PatternType = OfficeOpenXml.Style.ExcelFillStyle.Solid;
                    r.Style.Fill.BackgroundColor.SetColor(System.Drawing.Color.Black);
                }

                // format cells - add borders
                using (ExcelRange r = ws.Cells[StartFromRow + 1, 1, StartFromRow + dt.Rows.Count, dt.Columns.Count])
                {
                    r.Style.Border.Top.Style = ExcelBorderStyle.Thin;
                    r.Style.Border.Bottom.Style = ExcelBorderStyle.Thin;
                    r.Style.Border.Left.Style = ExcelBorderStyle.Thin;
                    r.Style.Border.Right.Style = ExcelBorderStyle.Thin;

                    r.Style.Border.Top.Color.SetColor(System.Drawing.Color.Black);
                    r.Style.Border.Bottom.Color.SetColor(System.Drawing.Color.Black);
                    r.Style.Border.Left.Color.SetColor(System.Drawing.Color.Black);
                    r.Style.Border.Right.Color.SetColor(System.Drawing.Color.Black);
                }

                // removed ignored columns
                for (int i = dt.Columns.Count - 1; i >= 0; i--)
                {
                    if (IgnoredColumns.Contains(dt.Columns[i].ColumnName))
                    {
                        ws.DeleteColumn(i + 1);
                    }
                }

                // add header and an additional column (left) and row (top)
                if (!String.IsNullOrEmpty(Heading))
                {
                    ws.Cells["A1"].Value = Heading;
                    ws.Cells["A1"].Style.Font.Size = 20;

                    ws.InsertColumn(1, 1);
                    ws.InsertRow(1, 1);
                    ws.Column(1).Width = 5;
                }

                result = pck.GetAsByteArray();
            }

            return result;
        }

        public static byte[] ExportExcel<T>(List<T> data, string Heading = "", params string[] IgnoredColumns)
        {
            return ExportExcel(ToDataTable<T>(data), Heading, IgnoredColumns);
        }
    }

通过这些，您可以将对象列表或数据表导出到 Excel 文件。此外，您可以指定要忽略的标题和列/属性（如ID）。此外，还添加了一些格式，并且小单元格将自动适应宽度。

使用此代码，您可以在需要 FileResult 的控制器操作中使用它：

 byte[] filecontent = ExcelExportHelper.ExportExcel(...);
 return File(filecontent, ExcelExportHelper.ExcelContentType, "FileName.xlsx");

我希望这会有所帮助！