Fixes in promisify, and DB code

chapter03/package-lock.json

@@ -4448,6 +4448,22 @@
                 "object-visit": "1.0.1"
             }
         },
+        "mariasql": {
+            "version": "0.2.6",
+            "resolved": "https://registry.npmjs.org/mariasql/-/mariasql-0.2.6.tgz",
+            "integrity": "sha1-q3iwZxFy8Or06A3a0Cm4A/Nc93o=",
+            "requires": {
+                "lru-cache": "2.7.3",
+                "nan": "2.10.0"
+            },
+            "dependencies": {
+                "lru-cache": {
+                    "version": "2.7.3",
+                    "resolved": "https://registry.npmjs.org/lru-cache/-/lru-cache-2.7.3.tgz",
+                    "integrity": "sha1-bUUk6LlV+V1PW1iFHOId1y+06VI="
+                }
+            }
+        },
         "md5": {
             "version": "2.2.1",
             "resolved": "https://registry.npmjs.org/md5/-/md5-2.2.1.tgz",
@@ -4566,9 +4582,7 @@
         "nan": {
             "version": "2.10.0",
             "resolved": "https://registry.npmjs.org/nan/-/nan-2.10.0.tgz",
-            "integrity": "sha512-bAdJv7fBLhWC+/Bls0Oza+mvTaNQtP+1RyhhhvD95pgUJz6XM5IzgmxOkItJ9tkoCiplvAnXI1tNmmUD/eScyA==",
-            "dev": true,
-            "optional": true
+            "integrity": "sha512-bAdJv7fBLhWC+/Bls0Oza+mvTaNQtP+1RyhhhvD95pgUJz6XM5IzgmxOkItJ9tkoCiplvAnXI1tNmmUD/eScyA=="
         },
         "nanomatch": {
             "version": "1.2.9",

chapter03/package.json

@@ -7,6 +7,7 @@
         "build": "flow-remove-types src/ -d out/",
         "buildWithMaps": "flow-remove-types src/ -d out/ --pretty --sourcemaps",
         "start": "npm run build && node out/doroundmath.js",
+        "start-db": "npm run build && node out/dbaccess.js",
         "nodemon": "nodemon --watch src --delay 1 --exec npm start",
         "addTypes": "flow-typed install",
         "update": "npm install && flow-typed install",
@@ -71,7 +72,8 @@
         "printWidth": 75
     },
     "dependencies": {
-        "axios": "^0.18.0"
+        "axios": "^0.18.0",
+        "mariasql": "^0.2.6"
     },
     "devDependencies": {
         "babel-eslint": "^8.2.2",

chapter03/src/dbaccess.js

@@ -0,0 +1,115 @@
+/* @flow */
+"use strict";
+
+const mariaSQL = require("mariasql");
+const { promisify } = require("util");
+
+const DB_HOST = "127.0.0.1";
+const DB_USER = "fkereki";
+const DB_PASS = "modernJS!!";
+const DB_SCHEMA = "world";
+
+async function tryDbAccess(dbConn) {
+    try {
+        const rows = await dbConn.query("SELECT 1960 AS someYear");
+        console.log(`Year was ${rows[0].someYear}`);
+    } catch (e) {
+        console.log("Unexpected error", e);
+    }
+}
+
+async function get10CountriesWithMoreCities(dbConn) {
+    try {
+        const myQuery = `SELECT 
+		    CI.countryCode, 
+		    CO.countryName, 
+		    COUNT(*) as countCities
+        FROM cities CI JOIN countries CO 
+		ON CI.countryCode=CO.countryCode
+        GROUP BY 1 
+		ORDER BY 3 DESC 
+		LIMIT 10`;
+
+        const rows = await dbConn.query(myQuery);
+        rows.forEach(r =>
+            console.log(r.countryCode, r.countryName, r.countCities)
+        );
+
+        /*
+            An alternative: return arrays instead of objects
+        */
+        const rows2 = await dbConn.query(myQuery, null, {
+            useArray: true
+        });
+        rows2.forEach(r => console.log(r[0], r[1], r[2]));
+    } catch (e) {
+        console.log("Unexpected error", e);
+    }
+}
+
+async function addSeekAndDeleteCountry(dbConn) {
+    try {
+        const code = "42";
+        const name = "DOUGLASADAMSLAND";
+
+        /*
+            1. Add the new country via a prepared insert statement
+        */
+
+        const prepInsert = dbConn.prepare(
+            "INSERT INTO countries (countryCode, countryName) VALUES (:code, :name)"
+        );
+        const preppedInsert = prepInsert({ code, name });
+        await dbConn.query(preppedInsert);
+
+        /*
+            1b. Alternative way, with placeholders
+        await dbConn.query(
+            "INSERT INTO countries (countryCode, countryName) VALUES (?, ?)",
+            [code, name]
+        );
+        */
+
+        /*
+            2. Seek the recently added country
+        */
+        const getAdams = `SELECT * FROM countries WHERE countryCode="${code}"`;
+        const adams = await dbConn.query(getAdams);
+        console.log(
+            adams.length,
+            adams[0].countryCode,
+            adams[0].countryName
+        );
+
+        /*
+            3. Drop the new country
+        */
+        await dbConn.query(`DELETE FROM countries WHERE countryCode="42"`);
+
+        /*
+            4. Verify that the country is no more
+        */
+        const adams2 = await dbConn.query(getAdams);
+        console.log(adams2.length);
+    } catch (e) {
+        console.log("Unexpected error", e);
+    }
+}
+
+function getDbConnection(host, user, password, db) {
+    const dbConn = new mariaSQL({ host, user, password, db });
+    dbConn.query = promisify(dbConn.query);
+    return dbConn;
+}
+
+const dbConn = getDbConnection(DB_HOST, DB_USER, DB_PASS, DB_SCHEMA);
+
+tryDbAccess(dbConn);
+
+get10CountriesWithMoreCities(dbConn);
+
+addSeekAndDeleteCountry(dbConn);
+
+/*
+    After everything is done, you can do dbConn.end()
+*/

chapter03/src/promisify.js

@@ -22,9 +22,10 @@ showFileLength1(FILE_TO_READ);
 // 2. Alternative style using promises
 
 function showFileLength2(fileName: string): void {
-    const readFile = util.promisify(fs.readFile);
+    fs.readFile = util.promisify(fs.readFile);
 
-    readFile(fileName, "utf8")
+    fs
+        .readFile(fileName, "utf8")
         .then((text: string) => {
             console.log(`2. Reading with promises: ${text.length} bytes`);
         })
@@ -37,10 +38,10 @@ showFileLength2(FILE_TO_READ);
 // 3. Using async/await, and with an arrow function just for variety
 
 const showFileLength3 = async (fileName: string) => {
-    const readFile = util.promisify(fs.readFile);
+    fs.readFile = util.promisify(fs.readFile);
 
     try {
-        const text: string = await readFile(fileName, "utf8");
+        const text: string = await fs.readFile(fileName, "utf8");
         console.log(`3. Reading with async/await: ${text.length} bytes`);
     } catch (err) {
         throw err;