some progress

node_modules/mongoose/lib/plugins/trackTransaction.js

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+'use strict';
+
+const arrayAtomicsSymbol = require('../helpers/symbols').arrayAtomicsSymbol;
+const sessionNewDocuments = require('../helpers/symbols').sessionNewDocuments;
+const utils = require('../utils');
+
+module.exports = function trackTransaction(schema) {
+  schema.pre('save', function trackTransactionPreSave() {
+    const session = this.$session();
+    if (session == null) {
+      return;
+    }
+    if (session.transaction == null || session[sessionNewDocuments] == null) {
+      return;
+    }
+
+    if (!session[sessionNewDocuments].has(this)) {
+      const initialState = {};
+      if (this.isNew) {
+        initialState.isNew = true;
+      }
+      if (this.$__schema.options.versionKey) {
+        initialState.versionKey = this.get(this.$__schema.options.versionKey);
+      }
+
+      initialState.modifiedPaths = new Set(Object.keys(this.$__.activePaths.getStatePaths('modify')));
+      initialState.atomics = _getAtomics(this);
+
+      session[sessionNewDocuments].set(this, initialState);
+    } else {
+      const state = session[sessionNewDocuments].get(this);
+
+      for (const path of Object.keys(this.$__.activePaths.getStatePaths('modify'))) {
+        state.modifiedPaths.add(path);
+      }
+      state.atomics = _getAtomics(this, state.atomics);
+    }
+  });
+};
+
+function _getAtomics(doc, previous) {
+  const pathToAtomics = new Map();
+  previous = previous || new Map();
+
+  const pathsToCheck = Object.keys(doc.$__.activePaths.init).concat(Object.keys(doc.$__.activePaths.modify));
+
+  for (const path of pathsToCheck) {
+    const val = doc.$__getValue(path);
+    if (val != null &&
+        Array.isArray(val) &&
+        utils.isMongooseDocumentArray(val) &&
+        val.length &&
+        val[arrayAtomicsSymbol] != null &&
+        Object.keys(val[arrayAtomicsSymbol]).length !== 0) {
+      const existing = previous.get(path) || {};
+      pathToAtomics.set(path, mergeAtomics(existing, val[arrayAtomicsSymbol]));
+    }
+  }
+
+  const dirty = doc.$__dirty();
+  for (const dirt of dirty) {
+    const path = dirt.path;
+
+    const val = dirt.value;
+    if (val != null && val[arrayAtomicsSymbol] != null && Object.keys(val[arrayAtomicsSymbol]).length !== 0) {
+      const existing = previous.get(path) || {};
+      pathToAtomics.set(path, mergeAtomics(existing, val[arrayAtomicsSymbol]));
+    }
+  }
+
+  return pathToAtomics;
+}
+
+function mergeAtomics(destination, source) {
+  destination = destination || {};
+
+  if (source.$pullAll != null) {
+    destination.$pullAll = (destination.$pullAll || []).concat(source.$pullAll);
+  }
+  if (source.$push != null) {
+    destination.$push = destination.$push || {};
+    destination.$push.$each = (destination.$push.$each || []).concat(source.$push.$each);
+  }
+  if (source.$addToSet != null) {
+    destination.$addToSet = (destination.$addToSet || []).concat(source.$addToSet);
+  }
+  if (source.$set != null) {
+    destination.$set = Object.assign(destination.$set || {}, source.$set);
+  }
+
+  return destination;
+}