MapType _copy function is not really compatible with Map object

[davyzhang]

MapType.prototype._copy = function (val, opts) {
  if (val && typeof val == 'object' && !Array.isArray(val)) {
    var values = this.valuesType;
    var keys = Object.keys(val);
    var i, l, key;
    var copy = {};
    for (i = 0, l = keys.length; i < l; i++) {
      key = keys[i];
      copy[key] = values._copy(val[key], opts);
    }
    return copy;
  }
  throwInvalidError(val, this);
};

If the val is a Map object, this function will copy nothing from the keys.

Can we change it to be compatible with the Map object by checking if it is Map first?

val instanceof Map

should do the trick

[davyzhang]

That won't be this simple if I try to deserialize the data to the Object or Map. I figure there's no way to make it consistent except adding another parameter

[mtth]

Hi @davyzhang. You can use a logical type to represent Avro maps as JS maps. For example something like:

/** A minimal logical type which represents Avro maps as JS maps. */
class MapType extends avro.types.LogicalType {
  _fromValue(obj) {
    return new Map(Object.entries(obj));
  }
  _toValue(map) {
    return map instanceof Map ? Object.fromEntries(map) : undefined;
  }
}

/** A type hook which applies the above logical type to all maps. */
function createTypeHook() {
  const seen = new Set();
  return (schema, opts) => {
    if (!schema || schema.type !== 'map' || seen.has(schema)) {
      return; // Fall back to default logic.
    }
    seen.add(schema);
    return new MapType(schema, opts);
  };
}

Sample usage:

const schema = {
  name: 'Test',
  type: 'record',
  fields: [
    {name: 'foo', type: {type: 'map', values: 'int'}},
  ],
};
const type = avro.Type.forSchema(schema, {typeHook: createTypeHook()});

const data = {foo: new Map([['a', 1]])};
console.log(type.isValid(data)); // true
console.log(type.clone(data).foo.get('a')); // 1

[davyzhang]

That's great! Thank you.