MSSQL to handle duplicated columns names like other DB clients (#42)

* only keep the last returned value per duplicated columns

* comments and more tests

Author: Sylvestre

lib/mssql.js

@@ -3,6 +3,7 @@ import JSONStream from "JSONStream";
 import {json} from "micro";
 import mssql from "mssql";
 import {failedCheck, badRequest, notImplemented} from "./errors.js";
+import {Transform} from "stream";
 
 const TYPES = mssql.TYPES;
 
@@ -64,36 +65,53 @@ export async function queryStream(req, res, pool) {
   try {
     await new Promise((resolve, reject) => {
       const request = new mssql.Request(db);
+      // We are using the arrayRowMode to handle potential duplicated column name.
+      // See: https://github.com/tediousjs/node-mssql#handling-duplicate-column-names
+      request.arrayRowMode = true;
       const stream = request.toReadableStream();
 
       params.forEach((param, idx) => {
         request.input(`${idx + 1}`, param);
       });
 
+      const columnNameMap = new Map();
       request.query(sql);
       request.once("recordset", () => clearInterval(keepAlive));
       request.on("recordset", (columns) => {
         const schema = {
           type: "array",
           items: {
             type: "object",
-            properties: Object.entries(columns).reduce(
-              (schema, [name, props]) => {
-                return {
-                  ...schema,
-                  ...{[name]: dataTypeSchema({type: props.type.name})},
-                };
-              },
-              {}
-            ),
+            properties: columns.reduce((schema, col, idx) => {
+              columnNameMap.set(idx, col.name);
+              return {
+                ...schema,
+                ...{[col.name]: dataTypeSchema({type: col.type.name})},
+              };
+            }, {}),
           },
         };
 
         res.write(`${JSON.stringify(schema)}`);
         res.write("\n");
       });
 
-      stream.pipe(JSONStream.stringify("", "\n", "\n")).pipe(res);
+      stream
+        .pipe(
+          new Transform({
+            objectMode: true,
+            transform(chunk, encoding, cb) {
+              const row = chunk.reduce((acc, r, idx) => {
+                const key = columnNameMap.get(idx);
+                return {...acc, [key]: r};
+              }, {});
+
+              cb(null, row);
+            },
+          })
+        )
+        .pipe(JSONStream.stringify("", "\n", "\n"))
+        .pipe(res);
       stream.on("done", () => {
         resolve();
       });

test/mssql.test.js

@@ -119,6 +119,67 @@ describe("mssql", () => {
           );
           expect(row).to.equal(JSON.stringify({CustomerID: testCustomerId}));
 
+          resolve();
+        }
+      });
+    });
+    it("should handle duplicated column names", () => {
+      return new Promise(async (resolve, reject) => {
+        const req = new MockReq({method: "POST", url: "/query-stream"}).end({
+          sql: "SELECT 1 as _a1, 2 as _a1 FROM test.SalesLT.SalesOrderDetail",
+          params: [],
+        });
+
+        const res = new MockRes(onEnd);
+
+        const index = mssql(credentials);
+        await index(req, res);
+
+        function onEnd() {
+          const [schema, row] = this._getString().split("\n");
+
+          expect(row).to.equal(
+            JSON.stringify({
+              _a1: 2,
+            })
+          );
+
+          resolve();
+        }
+      });
+    });
+    it("should select the last value of any detected duplicated columns", () => {
+      return new Promise(async (resolve, reject) => {
+        const req = new MockReq({method: "POST", url: "/query-stream"}).end({
+          sql: "SELECT TOP 1 ModifiedDate, ModifiedDate FROM test.SalesLT.SalesOrderDetail",
+          params: [],
+        });
+
+        const res = new MockRes(onEnd);
+
+        const index = mssql(credentials);
+        await index(req, res);
+
+        function onEnd() {
+          const [schema, row] = this._getString().split("\n");
+
+          expect(schema).to.equal(
+            JSON.stringify({
+              type: "array",
+              items: {
+                type: "object",
+                properties: {
+                  ModifiedDate: {type: ["null", "string"], date: true},
+                },
+              },
+            })
+          );
+          expect(row).to.equal(
+            JSON.stringify({
+              ModifiedDate: "2008-06-01T00:00:00.000Z",
+            })
+          );
+
           resolve();
         }
       });