HandleBars .Net If Comparision

Question

I use Handlebars .NET for my mail templates so i generate template at server side width ASP.NET MVC. I need a comparision like this. But it doest't work? What can I do?

//Product.ProdType is a enum property 

{{#if (Product.ProdType=='BlaBlaBla')}}
<p>This is a test</p>
{{/if}}

Answer 1

Logic like you're trying to do has to be in a helper function. You can't put relational operators like that directly into a handlebars template. It is designed that way on purpose. Helpers are very easy to create and use. See http://handlebarsjs.com/#helpers more more info.

hbs.registerHelper("IsSame", function(ProdType) {
 if(ProdType == "BlaBlaBla") {
   $('#HereText').append('<p>This is a test</p>');
    }
});

Do this in the template

<div class="row">
   {{IsSame Product.ProdType}}
</div>

so here you are passing your value to a helper function and doing your comparison..

Answer 2

I just added this package, and it magically started working as expected.

https://github.com/Handlebars-Net/Handlebars.Net.Extension.NewtonsoftJson

I am still using my normal C# class, but calling it in this way

model = new mydata(){...};
var handlebars = Handlebars.Create();
handlebars.Configuration.UseNewtonsoftJson();

var template = handlebars.Compile(source);
var output = template(model);

Answer 3

I'm using the Handlebars.NET author's way as committed in its unit tests and it works like a charm:

Handlebars.RegisterHelper("ifCond", (writer, options, context, arguments) =>
{
    if (arguments[0] == arguments[1])
    {
        options.Template(writer, (object)context);
    }
    else
    {
        options.Inverse(writer, (object)context);
    }
});

(at least in Handlebars.NET 1.10.1).

Answer 4

I had the same problem and I created a helper function "ifCond" that works with numeric data types and string. It can be optimized or expanded to work with other types.

Handlebars.RegisterHelper("ifCond",
        (writer, context, args) =>
        {
            if (args.Length != 5)
            {
                writer.Write("ifCond:Wrong number of arguments");
                return;
            }

            if (args[0] == null || args[0].GetType().Name == "UndefinedBindingResult")
            {
                writer.Write("ifCond:args[0] undefined");
                return;
            }
            if (args[1] == null || args[1].GetType().Name == "UndefinedBindingResult")
            {
                writer.Write("ifCond:args[1] undefined");
                return;
            }
            if (args[2] == null || args[2].GetType().Name == "UndefinedBindingResult")
            {
                writer.Write("ifCond:args[2] undefined");
                return;
            }

            if (args[0].GetType().Name == "String")
            {
                string val1 = args[0].ToString();
                string val2 = args[2].ToString();

                switch (args[1].ToString())
                {
                    case ">":
                        writer.Write(val1.Length > val2.Length ? args[3] : args[4]);
                        break;
                    case "=":
                    case "==":
                        writer.Write(val1 == val2 ? args[3] : args[4]);
                        break;
                    case "<":
                        writer.Write(val1.Length < val2.Length ? args[3] : args[4]);
                        break;
                    case "!=":
                    case "<>":
                        writer.Write(val1 != val2 ? args[3] : args[4]);
                        break;
                }
            }
            else
            {
                float val1 = float.Parse(args[0].ToString());
                float val2 = float.Parse(args[2].ToString());

                switch (args[1].ToString())
                {
                    case ">":
                        writer.Write(val1 > val2 ? args[3] : args[4]);
                        break;
                    case "=":
                    case "==":
                        writer.Write(val1 == val2 ? args[3] : args[4]);
                        break;
                    case "<":
                        writer.Write(val1 < val2 ? args[3] : args[4]);
                        break;
                    case "<=":
                        writer.Write(val1 <= val2 ? args[3] : args[4]);
                        break;
                    case ">=":
                        writer.Write(val1 >= val2 ? args[3] : args[4]);
                        break;
                    case "!=":
                    case "<>":
                        writer.Write(val1 != val2 ? args[3] : args[4]);
                        break;
                }
            }

And here are some Unit test explaining the usage :

var template = Handlebars.Compile("{{{ifCond test '>' 1 '>1' '<=1' }}}");
var data = new { test = 2 };
var result = template(data);
Assert.AreEqual(">1", result);

data = new { test = 0 };
result = template(data);
Assert.AreEqual("<=1", result);

template = Handlebars.Compile("{{{ifCond test '=' 1 'eq' 'not eq' }}}");
data = new { test = 1 };
result = template(data);
Assert.AreEqual("eq", result);

data = new { test = 0 };
result = template(data);
Assert.AreEqual("not eq", result);

template = Handlebars.Compile("{{{ifCond test '!=' 1 'diff' 'eq' }}}");
data = new { test = 2 };
result = template(data);
Assert.AreEqual("diff", result);

template = Handlebars.Compile("{{{ifCond str '!=' '' 'not empty' 'empty' }}}");
var datastr = new { str = "abc" };
result = template(datastr);
Assert.AreEqual("not empty", result);

template = Handlebars.Compile("{{{ifCond str '==' '' 'empty' 'not empty' }}}");
datastr = new { str = "" };
result = template(datastr);
Assert.AreEqual("empty", result);

Hope it helps, and I also hope for a better implementation, more elegant, my solution works but I think it can be done in a more concise way.

Here is a usage example with a Int32 value inside a template:

{{ifCond MycountVariable '>' 1 'more than one' 'one'}}

And here is a usage example with a String value inside a template:

{{ifCond MyStringVariable '!=' '' MyStringVariable 'empty value'}}

Answer 5

I tried @Matteo Conta's solution, but it does not support variables combine with text. So I tweaked it a bit for easier to use & better support variables.

Syntax

{{#ifCond arg1 condition arg2}}
       True clause {{variable}}
{{else}}
       False clause {{variable}}
{{/ifCond}}

Code

Handlebars.RegisterHelper("ifCond", (writer, options, context, args) => {
    if (args.Length != 3)
    {
        writer.Write("ifCond:Wrong number of arguments");
        return;
    }
    if (args[0] == null || args[0].GetType().Name == "UndefinedBindingResult")
    {
        writer.Write("ifCond:args[0] undefined");
        return;
    }
    if (args[1] == null || args[1].GetType().Name == "UndefinedBindingResult")
    {
        writer.Write("ifCond:args[1] undefined");
        return;
    }
    if (args[2] == null || args[2].GetType().Name == "UndefinedBindingResult")
    {
        writer.Write("ifCond:args[2] undefined");
        return;
    }
    if (args[0].GetType().Name == "String")
    {
        var val1 = args[0].ToString();
        var val2 = args[2].ToString();

        switch (args[1].ToString())
        {
            case ">":
                if (val1.Length > val2.Length)
                {
                    options.Template(writer, (object)context);
                }
                else
                {
                    options.Inverse(writer, (object)context);
                }
                break;
            case "=":
            case "==":
                if (val1 == val2)
                {
                    options.Template(writer, (object)context);
                }
                else
                {
                    options.Inverse(writer, (object)context);
                }
                break;
            case "<":
                if (val1.Length < val2.Length)
                {
                    options.Template(writer, (object)context);
                }
                else
                {
                    options.Inverse(writer, (object)context);
                }
                break;
            case "!=":
            case "<>":
                if (val1 != val2)
                {
                    options.Template(writer, (object)context);
                }
                else
                {
                    options.Inverse(writer, (object)context);
                }
                break;
        }
    }
    else
    {
        var val1 = float.Parse(args[0].ToString());
        var val2 = float.Parse(args[2].ToString());

        switch (args[1].ToString())
        {
            case ">":
                if (val1 > val2)
                {
                    options.Template(writer, (object)context);
                }
                else
                {
                    options.Inverse(writer, (object)context);
                }
                break;
            case "=":
            case "==":
                if (val1 == val2)
                {
                    options.Template(writer, (object)context);
                }
                else
                {
                    options.Inverse(writer, (object)context);
                }
                break;
            case "<":
                if (val1 < val2)
                {
                    options.Template(writer, (object)context);
                }
                else
                {
                    options.Inverse(writer, (object)context);
                }
                break;
            case "!=":
            case "<>":
                if (val1 != val2)
                {
                    options.Template(writer, (object)context);
                }
                else
                {
                    options.Inverse(writer, (object)context);
                }
                break;
        }
    }
});

Sample usages

var template = Handlebars.Compile(@"{{#ifCond arg1 '>' arg2}}{{arg1}} is greater than {{arg2}}{{else}}{{arg1}} is less than {{arg2}}{{/ifCond}}");
var data = new { arg1 = 2 , arg2 = 1};
var result = template(data);
Assert.Equal("2 is greater than 1", result);

data = new { arg1 = 1, arg2 = 2 };
result = template(data);
Assert.Equal("1 is less than 2", result);

template = Handlebars.Compile(@"{{#ifCond arg1 '<' arg2}}{{arg1}} is less than {{arg2}}{{else}}{{arg1}} is greater than {{arg2}}{{/ifCond}}");
data = new { arg1 = 2, arg2 = 1 };
result = template(data);
Assert.Equal("2 is greater than 1", result);

data = new { arg1 = 1, arg2 = 2 };
result = template(data);
Assert.Equal("1 is less than 2", result);

template = Handlebars.Compile(@"{{#ifCond arg1 '=' arg2}}{{arg1}} is eq to {{arg2}}{{else}}{{arg1}} is not eq to {{arg2}}{{/ifCond}}");
data = new { arg1 = 1, arg2 = 1 };
result = template(data);
Assert.Equal("1 is eq to 1", result);

data = new { arg1 = 2, arg2 = 1 };
result = template(data);
Assert.Equal("2 is not eq to 1", result);

template = Handlebars.Compile(@"{{#ifCond arg1 '!=' arg2}}{{arg1}} is not eq to {{arg2}}{{else}}{{arg1}} is eq to {{arg2}}{{/ifCond}}");
data = new { arg1 = 2, arg2 = 1 };
result = template(data);
Assert.Equal("2 is not eq to 1", result);

template = Handlebars.Compile(@"{{#ifCond str '!=' ''}}not empty{{else}}empty{{/ifCond}}");
var datastr = new { str = "abc" };
result = template(datastr);
Assert.Equal("not empty", result);

template = Handlebars.Compile(@"{{#ifCond str '==' ''}}empty{{else}}not empty{{/ifCond}}");
datastr = new { str = "" };
result = template(datastr);
Assert.Equal("empty", result);