How do m2a merge works ? (element type field should be generated once)

[tigrou-ux]

Hello B3rn475,

I try to understand how m2a work and I miss something. The following code throws "element type field should be generated once". I'd like the obj1, 2 and 3 to be merged into entity like

{
                id: "entity",
                type: "entity",
                attributes: {
                    elementnames : ["myelement1","myelement2","myelement3"]
                },
                metadata: {}
}

var extendModel = createExtender({
  type: {},
  relation: {},
  custom: {}
});

var buildModel = function() {
    var obj1 = {
        id: "partial-element-1",
        type: "partial-element",
        attributes: {
            elementname: "myelement1"
        },
        metadata: {}
    }
    var obj2 = {
        id: "partial-element-2",
        type: "partial-element",
        attributes: {
            elementname: "myelement2"
        },
        metadata: {}
    }
    var obj3 = {
        id: "partial-element-3",
        type: "partial-element",
        attributes: {
            elementname: "myelement3"
        },
        metadata:{}
    }
    return extendModel({
        elements: [obj1, obj2, obj3],
        relations: [],
        metadata: {}
    })
}
var transformer = createTransformer({
    element: [
        createRule(function(element, model) {
            return true;
        }, function(element, model) {
            var el = {
                id: "entity",
                type: "entity",
                attributes: {
                    elementnames : []
                },
                metadata: {}
            }
            el.attributes.elementnames.push(element.attributes.elementname)
            return {
                elements: [el],
                relations: [],
                metadata: {} 
            }
        })
    ]
}, 'm2a');
var model = buildModel();
console.log(util.inspect(model));
var modelTransformed = transformer(model);

Thank you !

[B3rn475]

The problem is that the type field is marked as Single in the m2a configuration.
Given this configuration the system is expecting your code to generate that field only once.

In your specific example the fix is relatively easy.

var transformer = createTransformer({
    model: [
        createRule(function(model) {
            return true;
        }, function(model) {
            return {
                elements: [{
                    id: "entity",
                    type: "entity",
                    attributes: {
                        elementnames : []  // Not required, but here for readability
                    },
                }],
            };
        })
    ],
    element: [
        createRule(function(element, model) {
            return true;
        }, function(element, model) {
            return {
                elements: [{
                    id: "entity",
                    attributes: {
                        elementnames : [element.attributes.elementname],
                    },
                }],
            };
        }),
    ],
}, 'm2a');

To be honest the requirement of the type field, which currently is Single (https://github.com/B3rn475/almostjs-core/blob/master/lib/reducer.js#L39), should be relaxed to a more general Same which accepts multiple values, but only if they are the same.

[tigrou-ux]

Thanks! I like your project, continue!

[B3rn475]

Let me know, if it solves your problem.

If you are building something interesting with ALMOsT.js, and you would like to shared, I'm thinking about adding a "Projects using ALMOsT.js" sections in the README.md