152 lines
6.9 KiB
Markdown
152 lines
6.9 KiB
Markdown
# mustache#
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An extension of the mustache text template engine for .NET.
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Download using NuGet: [mustache#](http://nuget.org/packages/mustache-sharp)
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## Overview
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Generating text has always been a chore. Either you're concatenating strings like a mad man or you're getting fancy with `StringBuilder`. Either way, the logic for conditionally including values or looping over a collection really obscures the intention of the code. A more declarative approach would improve your code big time. Hey, that's why server-side scripting got popular in the first place, right?
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[mustache](http://mustache.github.com/) is a really simple tool for generating text. .NET developers already had access to `String.Format` to accomplish pretty much the same thing. The only problem was that `String.Format` used indexes for placeholders: `Hello, {0}!!!`. **mustache** let you use meaningful names for placeholders: `Hello, {{name}}!!!`.
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**mustache** is a logic-less text generator. However, almost every time I've ever needed to generate text I needed to turn some of it on or off depending on a value. Not having the ability to turn things off usually meant going back to building my text in parts.
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Introducing [handlebars.js](http://handlebarsjs.com/)... If you've needed to generate any HTML templates, **handlebars.js** is a really awesome tool. Not only does it support an `if` and `each` tag, it lets you define your own tags! It also makes it easy to reference nested values `{{Customer.Address.ZipCode}}`.
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**mustache#** brings the power of **handlebars.js** to .NET and then takes it a little bit further. Not only does it support the same tags, it also handles whitespace intelligently. **mustache#** will automatically remove lines that contain nothing but whitespace and tags. This allows you to make text templates that are easy to read.
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Hello, {{Customer.Name}}
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{{#with Order}}
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{{#if LineItems}}
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Here is a summary of your previous order:
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{{#each LineItems}}
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{{ProductName}}: {{UnitPrice:C}} x {{Quantity}}
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{{/each}}
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Your total was {{Total:C}}.
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{{#else}}
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You do not have any recent purchases.
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{{/if}}
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{{/with}}
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Most of the lines in the previous example will never appear in the final output. This allows you to use **mustache#** to write templates for normal text, not just HTML/XML.
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## Placeholders
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The placeholders can be any valid identifier. These map to the property names in your classes.
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### Formatting Placeholders
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Each format item takes the following form and consists of the following components:
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{{identifier[,alignment][:formatString]}}
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The matching braces are required. Notice that they are double curly braces! The alignment and the format strings are optional and match the syntax accepted by `String.Format`. Refer to [String.Format](http://msdn.microsoft.com/en-us/library/system.string.format.aspx)'s documentation to learn more about the standard and custom format strings.
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### Placeholder Scope
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The indentifier is used to find a property with a matching name. If you want to print out the object itself, you can use the special identifier `this`.
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FormatCompiler compiler = new FormatCompiler();
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Generator generator = compiler.Compiler("Hello, {{this}}!!!");
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string result = generator.Render("Bob");
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Console.Out.WriteLine(result); // Hello, Bob!!!
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Some tags, such as `each` and `with`, change which object the values will be retrieved from.
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If a property with the placeholder name can't be found at the current scope, the name will be searched for at the next highest level.
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**mustache#** will automatically detect when an object is a dictionary and search for matching key. In this case, it still needs to be a valid identifier name.
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### Nested Placeholders
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If you want to grab a nested property, you can separate identifiers using `.`.
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{{Customer.Address.ZipCode}}
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## The 'if' tag
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The **if** tag allows you to conditionally include a block of text.
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Hello{{#if Name}}, {{Name}}{{/if}}!!!
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The block will be printed if:
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* The value is a non-empty string.
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* The value is a non-empty collection.
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* The value is a char and isn't the NULL char.
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* The value is a non-zero number.
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* The value evaluates to true.
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The **if** tag has complimentary **elif** and **else** tags. There can be as many **elif** tags as desired but the **else** tag must appear only once and after all other tags.
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{{#if Male}}Mr.{{#elif Married}}Mrs.{{#else}}Ms.{{/if}}
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## The 'each' tag
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If you need to print out a block of text for each item in a collection, use the **each** tag.
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{{#each Customers}}
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Hello, {{Name}}!!
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{{/each}}
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Within the context of the **each** block, the scope changes to the current item. So, in the example above, `Name` would refer to a property in the `Customer` class.
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## The 'with' tag
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Within a block of text, you may refer to a same top-level placeholder over and over. You can cut down the amount of text by using the **with** tag.
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{{#with Customer.Address}}
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{{FirstName}} {{LastName}}
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{{Line1}}
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{{#if Line2}}{{Line2}}{{/if}}
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{{#if Line3}}{{Line3}}{{/if}}
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{{City}} {{State}}, {{ZipCode}}
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{{/with}}
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Here, the `Customer.Address` property will be searched first for the placeholders. If a property cannot be found in the `Address` object, it will be searched for in the `Customer` object and on up.
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## Defining Your Own Tags
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If you need to define your own tags, **mustache#** has everything you need.
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Once you define your own tags, you can register them with the compiler using the `RegisterTag` method.
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FormatCompiler compiler = new FormatCompiler();
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compiler.RegisterTag(myTag);
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Your tag can be referenced within the template by leading its name with a `#`.
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Custom tags can take any number of parameters. Parameters can have default values if you don't want to pass them all the time. Arguments are passed by specifying a placeholder.
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### Multi-line Tags
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Here's an example of a tag that will make all of its content upper case:
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public class UpperTagDefinition : ContentTagDefinition
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{
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public UpperTagDefinition()
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: base(true)
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{
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}
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public override string Decorate(IFormatProvider provider, string innerText, Dictionary<string, object> arguments)
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{
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return innerText.ToUpper();
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}
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}
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### In-line Tags
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Here's an example of a tag that will join the items of a collection:
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public class JoinTagDefinition : InlineTagDefinition
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{
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public JoinTagDefinition()
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: base("join")
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{
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}
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protected override IEnumerable<TagParameter> GetParameters()
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{
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return new TagParameter[] { new TagParameter("collection") };
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}
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protected override string GetText(IFormatProvider provider, Dictionary<string, object> arguments)
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{
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IEnumerable collection = (IEnumerable)arguments["collection"];
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return String.Join(", ", collection.Cast<object>().Select(o => o.ToString()));
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}
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}
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