---
title: Knex SQL Builder
pagination_prev: demos/desktop/index
pagination_next: demos/local/index
sidebar_custom_props:
  sql: true
---

import current from '/version.js';
import CodeBlock from '@theme/CodeBlock';

:::note

This demo was last tested on 2023 April 19 with Knex 2.4.2 and `better-sqlite`.

:::

## Integration Details

#### Importing Data

`sheet_to_json` generates an array of objects. An `INSERT` statement can be
generated from each row object using `knex.insert`:

```js
const aoo = XLSX.utils.sheet_to_json(ws);
for(let i = 0; i < aoo.length; ++i) await knex.insert(aoo[i]).into(table_name);
```

#### Exporting Data

The result of a `SELECT` statement is an array of objects:

```js
const aoo = await knex.select("*").from(table_name);
const worksheet = XLSX.utils.json_to_sheet(aoo);
```

## Complete Example

1) Install dependencies:

<CodeBlock language="bash">{`\
npm i --save https://cdn.sheetjs.com/xlsx-${current}/xlsx-${current}.tgz knex better-sqlite3`}
</CodeBlock>

2) Download the [test file](https://sheetjs.com/pres.numbers)

```bash
curl -LO https://sheetjs.com/pres.numbers
```

3) Save the following utility script to `sheetjsknex.js`:

```js title="sheetjsknex.js"
const XLSX = require("xlsx");

// define mapping between determined types and Knex types
const PG = { "n": "float", "s": "text", "b": "boolean" };

async function ws_to_knex(knex, ws, table_name) {

  // generate an array of objects from the data
  const aoo = XLSX.utils.sheet_to_json(ws);

  // types will map column headers to types, while hdr holds headers in order
  const types = {}, hdr = [];

  // loop across each row object
  aoo.forEach(row =>
    // Object.entries returns a row of [key, value] pairs.  Loop across those
    Object.entries(row).forEach(([k,v]) => {

      // If this is first time seeing key, mark unknown and append header array
      if(!types[k]) { types[k] = "?"; hdr.push(k); }

      // skip null and undefined
      if(v == null) return;

      // check and resolve type
      switch(typeof v) {
        case "string": // strings are the broadest type
          types[k] = "s"; break;
        case "number": // if column is not string, number is the broadest type
          if(types[k] != "s") types[k] = "n"; break;
        case "boolean": // only mark boolean if column is unknown or boolean
          if("?b".includes(types[k])) types[k] = "b"; break;
        default: types[k] = "s"; break; // default to string type
      }
    })
  );

  await knex.schema.dropTableIfExists(table_name);

  // use column type info to create table
  await knex.schema.createTable(table_name, (table) => { hdr.forEach(h => { table[PG[types[h]] || "text"](h); }); });

  // insert each non-empty row object
  for(let i = 0; i < aoo.length; ++i) {
    if(!aoo[i] || !Object.keys(aoo[i]).length) continue;
    try { await knex.insert(aoo[i]).into(table_name); } catch(e) {}
  }
  return knex;
}

async function knex_to_ws(knex, table_name) {
  const aoo = await knex.select("*").from(table_name);
  return XLSX.utils.json_to_sheet(aoo);
}

module.exports = { ws_to_knex, knex_to_ws };
```

4) Save the following to `SheetJSKnexTest.js`:

```js title="SheetJSKnexTest.js"
const { ws_to_knex, knex_to_ws } = require("./sheetjsknex");
const Knex = require('knex');

/* read file and get first worksheet */
const XLSX = require("xlsx");
const oldwb = XLSX.readFile("pres.numbers");
const wsname = oldwb.SheetNames[0];
const oldws = oldwb.Sheets[wsname];

(async() => {
  /* open connection to SheetJSKnex.db */
  let knex = Knex({ client: 'better-sqlite3', connection: { filename: "SheetJSKnex.db" } });
  try {
    /* load data into database and close connection */
    await ws_to_knex(knex, oldws, "Test_Table");
  } finally { knex.destroy(); }

  /* reconnect to SheetJSKnex.db */
  knex = Knex({ client: 'better-sqlite3', connection: { filename: "SheetJSKnex.db" } });
  try {
    /* get data from db */
    const aoo = await knex.select("*").from("Test_Table");

    /* export to file */
    const newws = await knex_to_ws(knex, "Test_Table");
    const newwb = XLSX.utils.book_new();
    XLSX.utils.book_append_sheet(newwb, newws, "Export");
    XLSX.writeFile(newwb, "SheetJSKnex.xlsx");
  } finally { knex.destroy(); }
})();
```

This script will read `pres.numbers` and load data into a table `Test_Table`.
The SQLite database will be saved to `SheetJSKnex.db`.

After closing the connection, the script will make a new connection and export
data to `SheetJSKnex.xlsx`.

5) Run the script:

```bash
node SheetJSKnexTest.js
```

The script will generate two artifacts:

`SheetJSKnex.xlsx` can be opened in a spreadsheet app or tested in the terminal:

```bash
npx xlsx-cli SheetJSKnex.xlsx
```

`SheetJSKnex.db` can be verified with the `sqlite3` command line tool:

```bash
sqlite3 SheetJSKnex.db 'select * from Test_Table'
```