Merge pull request #306 from C2FO/issue272

Added appending to CSV example #272

Author: doug-martin

History.md

@@ -3,9 +3,11 @@
 * [ADDED] Ability to Transform Header [#287](https://github.com/C2FO/fast-csv/issues/287)
 * [ADDED] Example require and import to README [#301](https://github.com/C2FO/fast-csv/issues/301)
 * [ADDED] Added new formatting option `alwaysWriteHeaders` to always write headers even if no rows are provided [#300](https://github.com/C2FO/fast-csv/issues/300)
-* [FIXED] Issue with duplicate headers causing dataloss, duplicate headers will can an error to be emitted. [#276](https://github.com/C2FO/fast-csv/issues/276)
+* [ADDED] Appending to csv example and docs [#272](https://github.com/C2FO/fast-csv/issues/300)
+* [FIXED] Issue with duplicate headers causing dataloss, duplicate headers will can an error to be emitted. [#276](https://github.com/C2FO/fast-csv/issues/272)
 * [FIXED] Issue where an error thrown while processing rows causes stream continue to parse, causing duplicate writes or swallowed exceptions.
 
+
 # v3.6.0
 
 * [ADDED] `maxRows` option to limit the number of rows parsed. [#275](https://github.com/C2FO/fast-csv/issues/275) [#277](https://github.com/C2FO/fast-csv/pull/277) - [@cbrittingham](https://github.com/cbrittingham)

docs/formatting.md

@@ -26,6 +26,7 @@
     * [`quoteColumns`](#examples-quote-columns)
     * [`quoteHeaders`](#examples-quote-headers)
     * [Transforming Rows](#examples-transforming)
+    * [Appending To A CSV](#examples-appending)
 
 <a name="options"></a>
 ## Options
@@ -838,4 +839,88 @@ VALUE1A,VALUE2A
 VALUE1A,VALUE2A
 VALUE1A,VALUE2A
 VALUE1A,VALUE2A
+```
+
+<a name="examples-appending"></a>
+### Appending To A CSV
+
+[`examples/formatting/append.example.js`](../examples/formatting/append.example.js)
+
+In this example a new csv is created then appended to.
+
+```javascript
+const path = require('path');
+const fs = require('fs');
+
+const write = (filestream, rows, options) => {
+    return new Promise((res, rej) => {
+        csv.writeToStream(filestream, rows, options)
+            .on('error', err => rej(err))
+            .on('finish', () => res());
+    });
+};
+
+// create a new csv
+const createCsv = (filePath, rows) => {
+    const csvFile = fs.createWriteStream(filePath);
+    return write(csvFile, rows, { headers: true, includeEndRowDelimiter: true });
+};
+
+// append the rows to the csv
+const appendToCsv = (filePath, rows = []) => {
+    const csvFile = fs.createWriteStream(filePath, { flags: 'a' });
+    // notice how headers are set to false
+    return write(csvFile, rows, { headers: false });
+};
+
+// read the file
+const readFile = filePath => {
+    return new Promise((res, rej) => {
+        fs.readFile(filePath, (err, contents) => {
+            if (err) {
+                return rej(err);
+            }
+            return res(contents);
+        });
+    });
+};
+
+const csvFilePath = path.resolve(__dirname, 'tmp', 'append.csv');
+
+// 1. create the csv
+createCsv(csvFilePath, [
+    { a: 'a1', b: 'b1', c: 'c1' },
+    { a: 'a2', b: 'b2', c: 'c2' },
+    { a: 'a3', b: 'b3', c: 'c3' },
+])
+    .then(() => {
+        // 2. append to the csv
+        return appendToCsv(csvFilePath, [
+            { a: 'a4', b: 'b4', c: 'c4' },
+            { a: 'a5', b: 'b5', c: 'c5' },
+            { a: 'a6', b: 'b6', c: 'c6' },
+        ]);
+    })
+    .then(() => readFile(csvFilePath))
+    .then(contents => {
+        console.log(`${contents}`);
+    })
+    .catch(err => {
+        console.error(err.stack);
+        process.exit(1);
+    });
+
+
+```
+
+Expected output
+
+```
+a,b,c
+a1,b1,c1
+a2,b2,c2
+a3,b3,c3
+a4,b4,c4
+a5,b5,c5
+a6,b6,c6
 ```

examples/formatting/append.example.js

@@ -0,0 +1,61 @@
+const path = require('path');
+const fs = require('fs');
+const csv = require('../..');
+
+const write = (filestream, rows, options) => {
+    return new Promise((res, rej) => {
+        csv.writeToStream(filestream, rows, options)
+            .on('error', err => rej(err))
+            .on('finish', () => res());
+    });
+};
+
+// create a new csv
+const createCsv = (filePath, rows) => {
+    const csvFile = fs.createWriteStream(filePath);
+    return write(csvFile, rows, { headers: true, includeEndRowDelimiter: true });
+};
+
+// append the rows to the csv
+const appendToCsv = (filePath, rows = []) => {
+    const csvFile = fs.createWriteStream(filePath, { flags: 'a' });
+    // notice how headers are set to false
+    return write(csvFile, rows, { headers: false });
+};
+
+// read the file
+const readFile = filePath => {
+    return new Promise((res, rej) => {
+        fs.readFile(filePath, (err, contents) => {
+            if (err) {
+                return rej(err);
+            }
+            return res(contents);
+        });
+    });
+};
+
+const csvFilePath = path.resolve(__dirname, 'tmp', 'append.csv');
+
+// 1. create the csv
+createCsv(csvFilePath, [
+    { a: 'a1', b: 'b1', c: 'c1' },
+    { a: 'a2', b: 'b2', c: 'c2' },
+    { a: 'a3', b: 'b3', c: 'c3' },
+])
+    .then(() => {
+        // 2. append to the csv
+        return appendToCsv(csvFilePath, [
+            { a: 'a4', b: 'b4', c: 'c4' },
+            { a: 'a5', b: 'b5', c: 'c5' },
+            { a: 'a6', b: 'b6', c: 'c6' },
+        ]);
+    })
+    .then(() => readFile(csvFilePath))
+    .then(contents => {
+        console.log(`${contents}`);
+    })
+    .catch(err => {
+        console.error(err.stack);
+        process.exit(1);
+    });

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "fast-csv",
-  "version": "3.6.0",
+  "version": "3.7.0",
   "description": "CSV parser and writer",
   "main": "./build/src/index.js",
   "types": "./build/src/index.d.ts",