Implement generic expand and navigation feature

notes/srv/RemoteHandler.js

@@ -0,0 +1,252 @@
+function getEntity(absoluteName) {
+  const [serviceName, entityName] = absoluteName.split(".");
+  return cds.services[serviceName].entities[entityName];
+}
+
+function fixColumnName(entity, name) {
+  const fullName = `${entity.name}.${name}`;
+  return RemoteHandler.columnNameFixes[fullName] || name;
+}
+
+function associationLink(entity, associationName) {
+  const association = entity.associations[associationName];
+  const cardinalityMax = association.cardinality && association.cardinality.max;
+  if (!association)
+    throw new Error(
+      `Association "${associationName}" does not exists for entity "${entity.name}".`
+    );
+  if (association.keys) {
+    return associationKey(entity, association);
+  }
+
+  if (association.on && association.on.length === 3 && association.on[0].ref[0] === associationName && association.on[1] === "=" ) {
+    const keyFieldName = fixColumnName(entity, association.on[2].ref[0]);
+    const targetKeyFieldName = association.on[0].ref.slice(1).join("_");
+    return [keyFieldName, targetKeyFieldName, association.target, cardinalityMax];
+  }
+
+  if (association.on) {
+    const { reverseAssociationName } = associationOn(entity, association);
+    const targetEntity = getEntity(association.target);
+    const reverseAssociation =
+      targetEntity.associations[reverseAssociationName];
+    const [targetKeyFieldName, keyFieldName] = associationKey(
+      targetEntity,
+      reverseAssociation
+    );
+    return [keyFieldName, targetKeyFieldName, association.target, cardinalityMax];
+  }
+
+  throw new Error(
+    `Association "${associationName}" of entity "${entity.name}" has no "on" and no "keys".`
+  );
+}
+
+function associationOn(entity, association) {
+  if (
+    !association.on.length === 3 ||
+    association.on[1] !== "=" ||
+    association.on[2].ref[0] !== "$self"
+  )
+    throw new Error(
+      `Association "${association.name}" for "${entity.name}" has not the expected form.`
+    );
+
+  const reverseAssociationName = association.on[0].ref[1];
+  const [targetServiceName, targetEntityName] = association.target.split(".");
+  return { targetServiceName, targetEntityName, reverseAssociationName };
+}
+
+function associationKey(entity, association) {
+  const key = association.keys && association.keys[0];
+  if (!key)
+    throw new Error(
+      `Association "${association.name}" for entity "${entity.name}" has no keys.`
+    );
+  return [key["$generatedFieldName"], key.ref[0], association.target, association.cardinality.max];
+}
+
+class RemoteHandler {
+  constructor(service, remoteEntities) {
+
+    this.service = service;
+    this.remoteEntities = remoteEntities;
+  }
+
+  serviceFor(entityName) {
+    return this.remoteEntities[entityName] || this.service;
+  }
+
+  /**
+   * Expand "to one" associations with a single key field
+   *
+   * @param {*} req
+   * @param {*} next
+   * @param {*} associationName
+   * @param {*} targetService
+   * @param {*} headers
+   * @returns
+   */
+  async mixinExpand(req, result, expand) {
+    const associationName = expand.ref[0];
+
+    // Get association target
+    const [keyFieldName, targetKeyFieldName, targetEntityName, cardinalityMax] =
+      associationLink(req.target, associationName);
+
+    // Request all associated entities
+    // REVISIT: Still needed?
+    //const mock = !cds.env.requires.API_BUSINESS_PARTNER.credentials;
+    //const tx = mock ? BupaService.tx(req) : BupaService;
+    let ids = [];
+    if (Array.isArray(result)) {
+      ids = result.map((entry) => entry[keyFieldName]);
+    } else {
+      ids = [result[keyFieldName]];
+    }
+
+    // Take over columns from original query
+    const expandColumns = expand.expand.map((entry) => entry.ref[0]);
+    if (expandColumns.indexOf(targetKeyFieldName) < 0)
+      expandColumns.push(targetKeyFieldName);
+
+    const targetService = this.serviceFor(targetEntityName);
+
+    // Select target
+    const targetQuery = SELECT.from(targetEntityName)
+      .where({ [targetKeyFieldName]: ids })
+      .columns(expandColumns);
+    const targetResult = await targetService.run(targetQuery);
+
+    let targetResultMap;
+
+    switch (cardinalityMax) {
+      case '1':
+        targetResultMap = this.mixinExpand_to_1(targetResult, targetKeyFieldName);
+        break;
+      case '*':
+        targetResultMap = this.mixinExpand_to_many(targetResult, targetKeyFieldName);
+        break;
+      default:
+        throw new Error(`Association with cardinality may ${cardinalityMax} is not supported.`);
+    }
+
+    const resultArray = Array.isArray(result) ? result : [ result ];
+    for (const entry of resultArray) {
+      const id = entry[keyFieldName];
+      const targetEntry = targetResultMap[id];
+      if (targetEntry) entry[associationName] = targetEntry;
+    }
+  }
+
+  mixinExpand_to_1(targetResult, targetKeyFieldName) {
+    const targetResultMap = {};
+    for (const targetEntry of targetResult) {
+      const id = targetEntry[targetKeyFieldName];
+      targetResultMap[id] = targetEntry;
+    }
+
+    return targetResultMap;
+  }
+
+  mixinExpand_to_many(targetResult, targetKeyFieldName) {
+    const targetResultMap = {};
+    for (const targetEntry of targetResult) {
+      const id = targetEntry[targetKeyFieldName];
+      if (!targetResultMap[id]) targetResultMap[id] = [];
+      targetResultMap[id].push(targetEntry);
+    }
+
+    return targetResultMap;
+  }
+
+  async resolveNavigation(req, next) {
+    const select = req.query.SELECT;
+    if (select.from.ref.length !== 2) {
+      throw new Error(
+        `Unsupported navigation query with different than 2 entities in FROM clause.`
+      );
+    }
+
+    // Get target
+    const entityName = select.from.ref[0].id;
+    const entity = getEntity(entityName);
+
+    const [keyFieldName, targetKeyFieldName, targetEntityName] =
+      associationLink(entity, select.from.ref[1]);
+
+    const sourceService = this.serviceFor(entityName);
+    const targetService = this.serviceFor(targetEntityName);
+
+    const selectOne = SELECT.one([keyFieldName])
+      .from(entityName)
+      .where(select.from.ref[0].where);
+    const entry = await sourceService.run(selectOne);
+
+    const selectTarget = SELECT(req.query.SELECT.columns)
+      .from(targetEntityName)
+      .where({ [targetKeyFieldName]: entry[keyFieldName] });
+    return await targetService.run(selectTarget);
+  }
+
+  async handle(req, next) {
+    let doRequest;
+
+    if (
+      req.query.SELECT.from.ref.length > 1 &&
+      req.target.name !== req.query.SELECT.from.ref[0]
+    ) {
+      doRequest = () => this.resolveNavigation(req, next)
+    } else {
+        const targetService = this.serviceFor(req.target.name);
+        doRequest = targetService === this.service ?
+        next : () => targetService.run(req.query)
+    }
+
+    return this.resolveExpands(req, doRequest);
+  }
+
+  async resolveExpands(req, next) {
+    const select = req.query.SELECT;
+    const expandFilter = (column) => {
+      if (!column.expand) return false;
+      const associationName = column.ref[0];
+      const associationTargetName =
+        req.target.associations[associationName].target;
+      return (
+        this.remoteEntities[associationTargetName] !==
+        this.remoteEntities[req.target.name]
+      );
+    };
+
+    const expands = select.columns.filter(expandFilter);
+    select.columns = select.columns.filter((column) => !expandFilter(column));
+
+    if (expands.length === 0) return next();
+
+    for (const expand of expands) {
+      const associationName = expand.ref[0];
+      const [keyFieldName] = associationLink(req.target, associationName);
+
+      // Make sure id property is contained in select
+      if (
+        !select.columns.find((column) =>
+          column.ref.find((ref) => ref == keyFieldName)
+        )
+      )
+        select.columns.push({ ref: keyFieldName });
+    }
+
+    // Call service implementation
+    const result = await next();
+
+    await Promise.all(
+      expands.map((expand) => this.mixinExpand(req, result, expand))
+    );
+
+    return result;
+  }
+}
+
+RemoteHandler.columnNameFixes = {};
+module.exports = RemoteHandler;

notes/srv/notes-service.js

@@ -1,5 +1,7 @@
 const cds = require("@sap/cds");
 
+const RemoteHandler = require('./RemoteHandler');
+
 const s4apiKey = process.env.S4_APIKEY;
 if (!s4apiKey && cds.env.profiles.indexOf("sandbox") >= 0) {
   console.error(
@@ -13,11 +15,21 @@ module.exports = cds.service.impl(async function () {
 
   const bpService = await cds.connect.to("API_BUSINESS_PARTNER");
 
+  // TODO: This seems to be a bug in the compiler
+  RemoteHandler.columnNameFixes = { ["NotesService.Suppliers.BusinessPartner"]: "ID" };
+
   // REVISIT: This is a workaround for the missing capability to add headers to the service
   const bpServiceDelegate = {
     run: query => bpService.send({ query, headers: { APIKey: s4apiKey } })
   };
 
+  const remoteHandler = new RemoteHandler(this, { [Suppliers.name]: bpServiceDelegate });
+
+  this.on("READ", Suppliers, (req, next) => remoteHandler.handle(req, next) );
+  this.on("READ", Notes, (req, next) => remoteHandler.handle(req, next) );
+
+
+  /*
   // Suppliers?$expand=notes
   this.on("READ", Suppliers, async (req, next) => {
     const expandIndex = req.query.SELECT.columns.findIndex(
@@ -58,4 +70,6 @@ module.exports = cds.service.impl(async function () {
     return bpServiceDelegate.run(req.query);
   });
 
+  */
+
 });