Realm Mock backed by AsyncStorage to try to enable on-device debugging

realmMock.js

// https://github.com/realm/realm-js/issues/370#issuecomment-270849466

import { AsyncStorage } from "react-native"

const STORAGE_KEY = 'MockRealm';

export default class Realm {
  constructor(params) {
    this.schema = {};
    this.callbackList = [];
    this.data = {};
    this.schemaCallbackList = {};
    params.schema.forEach((schema) => {
      this.data[schema.name] = {};
    });
    params.schema.forEach((schema) => {
      this.schema[schema.name] = schema;
    });
    this.lastLookedUpModel = null;
    this.addListener(null, this.onChange.bind(this));
  }

  async load() {
    const storedDataString = await AsyncStorage.getItem(STORAGE_KEY);
    if (storedDataString) {
      const storedData = JSON.parse(storedDataString);
      if (storedData) {
        this.data = storedData;
        console.log('MockRealm#load storedData:', storedData, 'LOAD_END');
      }
    }
  }

  onChange() {
    console.log('MockRealm#onChange data:', this.data);
    AsyncStorage.setItem(STORAGE_KEY, JSON.stringify(this.data));
  }

  objects(schemaName) {
    this.lastLookedUpModel = schemaName;
    const objects = Object.values(this.data[schemaName]);
    objects.values = () => objects;
    objects.sorted = () => this.compareFunc ? objects.sort(this.compareFunc) : objects.sort();
    objects.addListener = (cb) => {
      if (this.schemaCallbackList[schemaName]) {
        this.schemaCallbackList[schemaName].push(cb);
      } else {
        this.schemaCallbackList[schemaName] = [cb];
      }
    };
    objects.removeListener = () => {};
    objects.filtered = this.filtered ? this.filtered.bind(this, schemaName) : () => objects;
    return objects;
  }

  write(fn) {
    this.writing = true;
    fn();
    this.writing = false;
  }

  create(schemaName, object) {
    const modelObject = object;
    console.log('mockRealm#create args:', arguments, 'schemaName:', schemaName);
    const properties = this.schema[schemaName].properties;
    Object.keys(properties).forEach((key) => {
      if (modelObject[key] && modelObject[key].model) {
        this.data[modelObject[key].model][modelObject[key].id] = this.create(
          modelObject[key].model, modelObject[key],
        );
      } else if (modelObject[key] && modelObject[key].length && modelObject[key][0].model) {
        modelObject[key].forEach((obj) => {
          this.data[modelObject[key][0].model][obj.id] = obj;
        });
        modelObject[key].filtered = this.filtered ? this.filtered : () => modelObject[key];
        modelObject[key].sorted = () => modelObject[key].sort();
      }
    });

    if (modelObject.id === undefined) {
      modelObject.id = modelObject.key;
    }

    this.data[schemaName][modelObject.id] = modelObject;
    if (this.writing) {
      if (this.schemaCallbackList[schemaName]) {
        this.schemaCallbackList[schemaName].forEach(cb => cb(schemaName, {
          insertions: { length: 1 },
          modifications: { length: 0 },
          deletions: { length: 0 },
        }));
      }
      this.callbackList.forEach((cb) => { cb(); });
    }
    return modelObject;
  }

  objectForPrimaryKey(model, id) {
    this.lastLookedUpModel = model;
    return this.data[model][id];
  }

  delete(object) {
    if (this.lastLookedUpModel || object.model) {
      const model = object.model ? object.model : this.lastLookedUpModel
      if (Array.isArray(object)) {
        object.forEach((item) => {
          delete this.data[model][item.id];
        });
      }
      delete this.data[model][object.id];
      if (this.writing) {
        if (this.schemaCallbackList[model]) {
          this.schemaCallbackList[model].forEach(cb => cb(model, {
            insertions: { length: 0 },
            modifications: { length: 0 },
            deletions: { length: 1 },
          }));
        }
        this.callbackList.forEach((cb) => { cb(); });
      }
    }
  }

  deleteAll() {
    Object.keys(this.schema).forEach((key) => {
      if (this.writing && this.schemaCallbackList[this.schema[key].name]) {
        this.schemaCallbackList[this.schema[key].name].forEach(cb => cb(key, {
          insertions: { length: 0 },
          modifications: { length: 0 },
          deletions: { length: Object.values(this.data[this.schema[key].name]).length },
        }));
      }
      this.data[this.schema[key].name] = {};
    });
    if (this.writing) this.callbackList.forEach((cb) => { cb(); });
  }

  addListener(event, callback) {
    this.callbackList.push(callback);
  }

  prepareData(schemaName, objects) {
    objects.forEach((object) => {
      this.create(schemaName, object);
    });
  }

  close() {
  }
}

Realm.deleteFile = () => {
  AsyncStorage.removeItem(STORAGE_KEY);
};

Realm.Object = class Object {
  isValid() { return true; }
};

This is based on realm 2.12.0. Requires #load to be called before use.