问题
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}}
回答1:
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'}}
回答2:
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..
回答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).
回答4:
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);
来源：https://stackoverflow.com/questions/30933956/handlebars-net-if-comparision