use dataloader to collect calls to DB fixes cap-js#30

Author: d060338

lib/change-log.js

@@ -167,12 +167,12 @@ const _getChildChangeObjId = async function (
 const _formatCompositionContext = async function (changes, reqData) {
   const childNodeChanges = []
 
-  for (const change of changes) {
+  await Promise.all(changes.map(async (change) => {
     if (typeof change.valueChangedTo === "object") {
       if (!Array.isArray(change.valueChangedTo)) {
         change.valueChangedTo = [change.valueChangedTo]
       }
-      for (const childNodeChange of change.valueChangedTo) {
+      await Promise.all(change.valueChangedTo.map(async (childNodeChange) => {
         const curChange = Object.assign({}, change)
         const path = childNodeChange._path.split('/')
         const curNodePathVal = path.pop()
@@ -184,10 +184,10 @@ const _formatCompositionContext = async function (changes, reqData) {
           reqData
         )
         _formatCompositionValue(curChange, objId, childNodeChange, childNodeChanges)
-      }
+      }))
       change.valueChangedTo = undefined
     }
-  }
+  }))
   changes.push(...childNodeChanges)
 }
 
@@ -248,7 +248,7 @@ const _getObjectIdByPath = async function (
 
 const _formatObjectID = async function (changes, reqData) {
   const objectIdCache = new Map()
-  for (const change of changes) {
+  await Promise.all(changes.map(async (change) => {
     const path = change.serviceEntityPath.split('/')
     const curNodePathVal = path.pop()
     const parentNodePathVal = path.pop()
@@ -276,7 +276,7 @@ const _formatObjectID = async function (changes, reqData) {
     change.entityID = curNodeObjId
     change.parentEntityID = parentNodeObjId
     change.parentKey = getUUIDFromPathVal(parentNodePathVal)
-  }
+  }))
 }
 
 const _isCompositionContextPath = function (aPath, hasComp) {
@@ -290,6 +290,7 @@ const _isCompositionContextPath = function (aPath, hasComp) {
 }
 
 const _formatChangeLog = async function (changes, req) {
+  cds.context.dataloaders = {}
   await _formatObjectID(changes, req.data)
   await _formatAssociationContext(changes, req.data)
   await _formatCompositionContext(changes, req.data)
@@ -317,9 +318,9 @@ function _trackedChanges4 (srv, target, diff) {
       if (from === to) return
 
       /**
-       * 
-       * For the Inline entity such as Items, 
-       * further filtering is required on the keys 
+       *
+       * For the Inline entity such as Items,
+       * further filtering is required on the keys
        * within the 'association' and 'foreign key' to ultimately retain the keys of the entity itself.
        * entity Order : cuid {
        *   title      : String;

lib/entity-helper.js

@@ -1,4 +1,5 @@
 const cds = require("@sap/cds")
+const DataLoader = require("dataloader");
 const LOG = cds.log("change-log")
 
 
@@ -22,18 +23,28 @@ const getEntityByContextPath = function (aPath, hasComp = false) {
 
 const getObjIdElementNamesInArray = function (elements) {
   if (Array.isArray(elements)) return elements.map(e => {
-    const splitted = (e["="]||e).split('.')
+    const splitted = (e["="] || e).split('.')
     splitted.shift()
     return splitted.join('.')
   })
   else return []
 }
 
-const getCurObjFromDbQuery = async function (entityName, queryVal, /**optional*/ queryKey='ID') {
+const getCurObjFromDbQuery = async function (entityName, queryVal, /**optional*/ queryKey = 'ID') {
+  if (!(entityName in cds.context.dataloaders)) {
+    cds.context.dataloaders[entityName] = new DataLoader(async (keys) => {
+      // REVISIT: This always reads all elements -> should read required ones only!
+      const results = await SELECT.from(entityName).where(queryKey, 'in', keys)
+      const resultsByKey = results.reduce((acc, instance) => {
+        const key = instance[queryKey]
+        acc[key] = instance
+        return acc
+      }, {})
+      return keys.map(key => resultsByKey[key] || {})
+    })
+  }
   if (!queryVal) return {}
-  // REVISIT: This always reads all elements -> should read required ones only!
-  const obj = await SELECT.one.from(entityName).where({[queryKey]: queryVal})
-  return obj || {}
+  return cds.context.dataloaders[entityName].load(queryVal)
 }
 
 const getCurObjFromReqData = function (reqData, nodePathVal, pathVal) {
@@ -71,21 +82,22 @@ const getCurObjFromReqData = function (reqData, nodePathVal, pathVal) {
 }
 
 
-async function getObjectId (reqData, entityName, fields, curObj) {
-  let all = [], { curObjFromReqData: req_data={}, curObjFromDbQuery: db_data={} } = curObj
+async function getObjectId(reqData, entityName, fields, curObj) {
+  let all = [], {curObjFromReqData: req_data = {}, curObjFromDbQuery: db_data = {}} = curObj
   let entity = cds.model.definitions[entityName]
   if (!fields?.length) fields = entity["@changelog"]?.map?.(k => k['='] || k) || []
   for (let field of fields) {
     let path = field.split('.')
     if (path.length > 1) {
       let current = entity, _db_data = db_data
       while (path.length > 1) {
-        let assoc = current.elements[path[0]]; if (!assoc?.isAssociation) break
+        let assoc = current.elements[path[0]];
+        if (!assoc?.isAssociation) break
         let foreignKey = assoc.keys?.[0]?.$generatedFieldName
         let IDval =
-        req_data[foreignKey] && current.name === entityName
-          ? req_data[foreignKey]
-          : _db_data[foreignKey]
+          req_data[foreignKey] && current.name === entityName
+            ? req_data[foreignKey]
+            : _db_data[foreignKey]
         if (!IDval) {
           _db_data = {};
         } else try {
@@ -125,19 +137,18 @@ async function getObjectId (reqData, entityName, fields, curObj) {
 }
 
 
-
 const getDBEntity = (entity) => {
   if (typeof entity === 'string') entity = cds.model.definitions[entity]
   let proto = Reflect.getPrototypeOf(entity)
   if (proto instanceof cds.entity) return proto
 }
 
 const getValueEntityType = function (entityName, fields) {
-  const types=[], entity = cds.model.definitions[entityName]
+  const types = [], entity = cds.model.definitions[entityName]
   for (let field of fields) {
     let current = entity, path = field.split('.')
     if (path.length > 1) {
-      for (;;) {
+      for (; ;) {
         let target = current.elements[path[0]]?._target
         if (target) current = target; else break
         path.shift()
@@ -167,20 +178,20 @@ const hasComposition = function (parentEntity, subEntity) {
 }
 
 const _getCompositionObjFromReq = function (obj, targetID) {
-    if (obj?.ID === targetID) {
-        return obj;
-    }
+  if (obj?.ID === targetID) {
+    return obj;
+  }
 
-    for (const key in obj) {
-        if (typeof obj[key] === "object" && obj[key] !== null) {
-            const result = _getCompositionObjFromReq(obj[key], targetID);
-            if (result) {
-                return result;
-            }
-        }
+  for (const key in obj) {
+    if (typeof obj[key] === "object" && obj[key] !== null) {
+      const result = _getCompositionObjFromReq(obj[key], targetID);
+      if (result) {
+        return result;
+      }
     }
+  }
 
-    return null;
+  return null;
 };
 
 module.exports = {

package.json

@@ -37,5 +37,8 @@
         "model": "@cap-js/change-tracking"
       }
     }
+  },
+  "dependencies": {
+    "dataloader": "^2.2.2"
   }
 }