Optional attributes with custom snippet

[melwas]

Hi,

I have a custom snippet as below:

|===
|Path|Type|Description|Constraints

{{#fields}}

|{{#tableCellContent}}{{path}}{{/tableCellContent}}
|{{#tableCellContent}}{{type}}{{/tableCellContent}}
|{{#tableCellContent}}{{description}}{{/tableCellContent}}
|{{#tableCellContent}}{{constraints}}{{/tableCellContent}}

{{/fields}}
|===

When I set the attribute "constraints" for each field in request fields snippet in Test like this:

key("constraints") .value("Format: YYYY-MM-DD'T'HH:mm:ssZ"))

it works, but when even one field is missing constraints attribute the whole suite fails with:

org.springframework.restdocs.mustache.MustacheException$Context: No method or field with name 'constraints' on line 8
    at org.springframework.restdocs.mustache.Template.checkForMissing(Template.java:270)
    at org.springframework.restdocs.mustache.Template.getValue(Template.java:178)
    at org.springframework.restdocs.mustache.Template.getValueOrDefault(Template.java:223)
    at org.springframework.restdocs.mustache.Mustache$VariableSegment.execute(Mustache.java:787)
    at org.springframework.restdocs.mustache.Template$1.execute(Template.java:131)
    at org.springframework.restdocs.mustache.Template$1.execute(Template.java:124)
    at org.springframework.restdocs.mustache.Template$Fragment.execute(Template.java:59)
    at org.springframework.restdocs.templates.mustache.AsciidoctorTableCellContentLambda.execute(AsciidoctorTableCellContentLambda.java:36)

How to fix this?

[wilkinsona]

There are a couple of approaches you could take.

You could subclass RequestFieldsSnippet and override createModelFromDescriptor to add a default value for the constraints attribute.

Alternatively, you need to tell Mustache to use a default value when an entry in a template can't be resolved. Unfortunately, Mustache doesn't provide support for doing that in the template itself so you need to configure its compiler with a default value. You can do that like this:

MustacheTemplateEngine templateEngine = new MustacheTemplateEngine(
        new StandardTemplateResourceResolver(TemplateFormats.asciidoctor()),
        Mustache.compiler().escapeHTML(false).defaultValue(""));
MockMvcRestDocumentationConfigurer configurer = new MockMvcRestDocumentationConfigurer(
        this.restDocumentation).templateEngine(templateEngine);
MockMvc mockMvc = MockMvcBuilders.webAppContextSetup(this.context)
        .apply(configurer).build();

[tasosz]

On the snippet above, I've found that you need an extra parameter to the Mustache template engine constructor. Without it I was getting some documentation, but all table cells were empty of values.

Map<String, Object> templateContext = new HashMap<>();
templateContext.put("tableCellContent", new AsciidoctorTableCellContentLambda());

MustacheTemplateEngine templateEngine = new MustacheTemplateEngine(
        new StandardTemplateResourceResolver(TemplateFormats.asciidoctor()),
        Mustache.compiler().escapeHTML(false).defaultValue(""), templateContext);

[helpermethod]

Hi, for anyone reading this:

There IS actually a way to expand the constraints attribute to an empty string in case it's missing

{{#constraints}}{{.}}{{/constraints}}

This will output the value if it exists and an empty string if not.

[wilkinsona]

That's a neat trick, @helpermethod. Thank you.

For anyone else who, like me, was wondering how it works, . is a special variable that's the equivalent of this and #constraints is a section. When constraints exists in the model and isn't false or an empty list, whatever is within the section is rendered. In this case, the contents of the section are a reference to this which is the value of the constraints entry in the model. When constraints does not exist, the content of the section is skipped.