Add property usePrebuiltEmptyResultObjects to Query constructor which generates pre-shaped result rows

Author: HZ111 / Dev2

packages/pg/lib/query.js

@@ -24,13 +24,14 @@ class Query extends EventEmitter {
     if (process.domain && config.callback) {
       this.callback = process.domain.bind(config.callback)
     }
+    this.usePrebuiltEmptyResultObjects = config.usePrebuiltEmptyResultObjects == true
     this._result = new Result(this._rowMode, this.types)
-
     // potential for multiple results
     this._results = this._result
     this.isPreparedStatement = false
     this._canceledDueToError = false
     this._promise = null
+    this._prebuiltEmptyResultObject = null
   }
 
   requiresPreparation() {
@@ -64,6 +65,7 @@ class Query extends EventEmitter {
       }
       this._result = new Result(this._rowMode, this.types)
       this._results.push(this._result)
+      this._prebuiltEmptyResultObject = null
     }
   }
 
@@ -83,8 +85,12 @@ class Query extends EventEmitter {
       return
     }
 
+    if (this.usePrebuiltEmptyResultObjects && !this._prebuiltEmptyResultObject) {
+      this._createPrebuiltEmptyResultObject()
+    }
+
     try {
-      row = this._result.parseRow(msg.fields)
+      row = this._result.parseRow(msg.fields, this.usePrebuiltEmptyResultObjects ? { ... this._prebuiltEmptyResultObject } : {})
     } catch (err) {
       this._canceledDueToError = err
       return
@@ -138,7 +144,7 @@ class Query extends EventEmitter {
       try {
         this.callback(null, this._results)
       }
-      catch(err) {
+      catch (err) {
         process.nextTick(() => {
           throw err
         })
@@ -236,6 +242,13 @@ class Query extends EventEmitter {
   handleCopyData(msg, connection) {
     // noop
   }
+  _createPrebuiltEmptyResultObject() {
+    var row = {};
+    for (var i = 0; i < this._result.fields.length; i++) {
+      row[this._result.fields[i].name] = null
+    }
+    this._prebuiltEmptyResultObject = row
+  }
 }
 
-module.exports = Query
+module.exports = Query

packages/pg/lib/result.js

@@ -59,8 +59,7 @@ class Result {
     return row
   }
 
-  parseRow(rowData) {
-    var row = {}
+  parseRow(rowData, row = {}) {
     for (var i = 0, len = rowData.length; i < len; i++) {
       var rawValue = rowData[i]
       var field = this.fields[i].name

packages/pg/test/integration/gh-issues/3042-tests.js

@@ -0,0 +1,51 @@
+'use strict'
+const helper = require('../test-helper')
+
+const suite = new helper.Suite()
+
+// https://github.com/brianc/node-postgres/issues/2716
+suite.testAsync('rows returned from pg have a clean shape which allows faster access and copying', async () => {
+	const amountOfCols = 100
+	const testCopies = 10000
+	const expectedFasterFactor = 50
+
+	const client = new helper.pg.Client()
+	await client.connect()
+	
+	
+	const queryFields = []
+	for (let i = 1; i <= amountOfCols; i++) {
+		queryFields.push(`${i} as col${i}`)
+	}
+	const query = `SELECT ${queryFields.join(', ')}`
+	const resultWithoutShape = await client.query({
+		text: query,
+		usePrebuiltEmptyResultObjects: false
+	})
+	const rowFromPgWithoutShape = resultWithoutShape.rows[0]
+	const resultWithShape = await client.query({
+		text: query,
+		usePrebuiltEmptyResultObjects: true
+	})
+	const rowFromPgWithShape = resultWithShape.rows[0]
+	
+	
+	const beforeWithout = process.hrtime.bigint()
+	for (let i = 0; i < testCopies; i++) {
+		let copy = { ...rowFromPgWithoutShape }
+	}
+	const afterWithout = process.hrtime.bigint()
+	const withoutResult = afterWithout - beforeWithout
+
+	const beforeWith = process.hrtime.bigint()
+	for (let i = 0; i < testCopies; i++) {
+		let copy = { ...rowFromPgWithShape }
+	}
+	const afterWith = process.hrtime.bigint()
+	const withResult = afterWith - beforeWith
+
+	const factorFaster = withoutResult / withResult
+	assert(factorFaster > expectedFasterFactor)
+
+	await client.end()
+})