Add table generator post

src/posts/TableAutoGenerator.md

@@ -0,0 +1,138 @@
+---
+title: ASP.NET Core Table Generator
+description: A tag helper that takes a list and generates a table
+tags: [ Programming, C#, ASP.NET Core ]
+---
+
+This tag helper takes any `IEnumerable` and will use reflection to generate a table for it. This will pick up on attributes in the model for customizing the output.
+
+## How To Use
+
+The model in the `IEnumerable`:
+
+```csharp
+public class Thing
+{
+	// Don't make a column for this property
+	[Display(AutoGenerateField = false)]
+	public int ThingId { get; set; }
+
+	// Use "Thing Name" for the column header instead of "ThingName"
+	[Display(Name = "Thing Name")]
+	public string ThingName { get; set; }
+
+	// Use string.Format with the DataFormatString
+	[DisplayFormat(DataFormatString = "{0:C}")]
+	public decimal Price { get; set; }
+}
+```
+
+Then use the tag helper in the view:
+
+```cshtml
+<table asp-for="Things"></table>
+```
+
+## Code
+
+The tag helper:
+
+```csharp
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Mvc.ViewFeatures;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using System.ComponentModel.DataAnnotations;
+using System.Reflection;
+
+/// <summary>
+/// When the <see cref="For"/> is a list, fill the table with the list data with
+/// columns for each property.
+/// <para>
+/// Properties can be hidden from the table by adding <c>[Diaplay(AutoGenerateField = false)]</c>
+/// </para>
+/// <para>
+/// The column heading for each property is the property name by default. This can be overriden by
+/// adding <c>[Display(Name = "Property Name")]</c>
+/// </para>
+/// </summary>
+[HtmlTargetElement("table", Attributes = "asp-for")]
+public class TableTagHelper : TagHelper
+{
+	[HtmlAttributeName("asp-for")]
+	public ModelExpression For { get; set; }
+
+	public override void Process(TagHelperContext context, TagHelperOutput output)
+	{
+		var modelType = this.For.ModelExplorer.ModelType.GenericTypeArguments[0];
+		var list = this.For.Model as IEnumerable<object>;
+
+		if (list is null)
+			output.TagName = "";
+
+		// Don't display properties that have AutoGenerateField set to false
+		IList<PropertyInfo> properties = modelType.GetProperties()
+			.Where(p => !p.GetCustomAttributes<DisplayAttribute>(false)
+				.Any(a => a.GetAutoGenerateField() == false))
+			.ToList();
+
+		// Header row
+		List<TagBuilder> tableHeadCells = properties
+			.Select(p =>
+			{
+				string displayName = p.GetCustomAttributes<DisplayAttribute>(false)
+					.Where(a => !string.IsNullOrEmpty(a.GetName()))
+					.FirstOrDefault()
+					?.GetName()
+					?? p.Name;
+
+				TagBuilder th = new("th");
+				th.InnerHtml.Append(displayName);
+
+				return th;
+			})
+			.ToList();
+
+		TagBuilder theadTr = new("tr");
+		tableHeadCells.ForEach(th => theadTr.InnerHtml.AppendHtml(th));
+
+		TagBuilder thead = new("thead");
+		thead.InnerHtml.AppendHtml(theadTr);
+		output.Content.AppendHtml(thead);
+
+
+		// Content rows
+		List<TagBuilder> tableRows = list
+			.Select(item =>
+			{
+				List<TagBuilder> cells = properties
+					.Select(p =>
+					{
+						TagBuilder td = new("td");
+
+						var content = p.GetValue(item);
+						string dataFormatString = p.GetCustomAttributes<DisplayFormatAttribute>(false)
+							.Where(a => !string.IsNullOrWhiteSpace(a.DataFormatString))
+							.Select(a => a.DataFormatString)
+							.FirstOrDefault();
+
+						if (dataFormatString is not null)
+							td.InnerHtml.Append(string.Format(dataFormatString, content));
+						else if (content is not null)
+							td.InnerHtml.Append(content.ToString());
+
+						return td;
+					})
+					.ToList();
+
+				TagBuilder tr = new("tr");
+				cells.ForEach(td => tr.InnerHtml.AppendHtml(td));
+				return tr;
+			})
+			.ToList();
+
+		TagBuilder tbody = new("tbody");
+		tableRows.ForEach(tr => tbody.InnerHtml.AppendHtml(tr));
+		output.Content.AppendHtml(tbody);
+	}
+}
+```