docs.sheetjs.com/docz/docs/03-demos/23-data/14-knex.md

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KnexJS is a SQL query builder with support for a number of SQL dialects.

SheetJS is a JavaScript library for reading and writing data from spreadsheets.

This demo uses KnexJS and SheetJS to exchange data between spreadsheets and SQL servers. We'll explore how to use save tables from a database to spreadsheets and how to add data from spreadsheets into a database.

:::note Tested Deployments

This demo was tested in the following environments:

Version	Database	Connector Module	Date
2.5.1	SQLite	better-sqlite	2023-12-04
3.0.1	SQLite	better-sqlite	2023-12-04

:::

Integration Details

The SheetJS NodeJS module can be loaded in NodeJS scripts that use KnexJS.

Exporting Data

The KnexJS select method¹ creates a SELECT query. The return value is a Promise that resolves to an array of objects.

The SheetJS json_to_sheet method² can generate a worksheet object³ from the array of objects:

const table_name = "Tabeller1"; // name of table

/* fetch all data from specified table */
const aoo = await knex.select("*").from(table_name);

/* generate a SheetJS worksheet object from the data */
const worksheet = XLSX.utils.json_to_sheet(aoo);

A workbook object can be built from the worksheet using utility functions⁴. The workbook can be exported using the SheetJS writeFile method⁵:

/* create a new workbook and add the worksheet */
const wb = XLSX.utils.book_new();
XLSX.utils.book_append_sheet(wb, worksheet, "Sheet1");

/* export workbook to XLSX */
XLSX.writeFile(wb, "SheetJSKnexJSExport.xlsx");

Importing Data

The SheetJS sheet_to_json function⁶ takes a worksheet object and generates an array of objects.

The KnexJS insert method⁷ creates INSERT queries. The return value is a Promise that resolves when the query is executed:

const table_name = "Blatte1"; // name of table

/* generate an array of arrays from the worksheet */
const aoo = XLSX.utils.sheet_to_json(ws);

/* insert every row into the specified database table */
await knex.insert(aoo).into(table_name);

Creating a Table

The KnexJS Schema Builder supports creating tables with createTable⁸ and dropping tables with dropTableIfExists⁹.

The array of objects can be scanned to determine column names and types.

Implementation Details (click to show)

The aoo_to_knex_table function:

• scans each row object to determine column names and types
• drops and creates a new table with the determined column names and types
• loads the entire dataset into the new table

/* create table and load data given an array of objects and a Knex connection */
async function aoo_to_knex_table(knex, aoo, table_name) {
  /* define types that can be converted (e.g. boolean can be stored in float) */
  const T_FLOAT = ["float", "boolean"];
  const T_BOOL = ["boolean"];

  /* types is a map from column headers to Knex schema column type */
  const types = {};

  /* names is an ordered list of the column header names */
  const names = [];

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

      /* If this is first occurrence, mark unknown and append header to names */
      if(!types[k]) { types[k] = ""; names.push(k); }

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

      /* check and resolve type */
      switch(typeof v) {
        /* change type if it is empty or can be stored in a float */
        case "number": if(!types[k] || T_FLOAT.includes(types[k])) types[k] = "float"; break;
        /* change type if it is empty or can be stored in a boolean */
        case "boolean": if(!types[k] || T_BOOL.includes(types[k])) types[k] = "boolean"; break;
        /* no other type can hold strings */
        case "string": types[k] = "text"; break;
        default: types[k] = "text"; break;
      }
    })
  );

  /* Delete table if it exists in the DB */
  await knex.schema.dropTableIfExists(table_name);

  /* use column type info to create table */
  await knex.schema.createTable(table_name, (table) => {
    names.forEach(h => {
      /* call schema function e.g. table.text("Name"); table.float("Index"); */
      table[types[h] || "text"](h);
    });
  });

  /* insert each row */
  await knex.insert(aoo).into(table_name);
  return knex;
}

:::note pass

The Knex constructor may display a warning when connecting to SQLite:

sqlite does not support inserting default values. Set the `useNullAsDefault` flag to hide this warning. (see docs https://knexjs.org/guide/query-builder.html#insert).

That flag should be added to the options argument:

const Knex = require('knex');
let knex = Knex({
  client: 'better-sqlite3',
  connection: { filename: "SheetJSKnex.db" },
  // highlight-next-line
  useNullAsDefault: true
});

:::

Complete Example

1. Install dependencies:

{\ npm i --save https://cdn.sheetjs.com/xlsx-${current}/xlsx-${current}.tgz knex better-sqlite3}

2. Download the test file

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

3. Download SheetJSKnexTest.js:

curl -LO https://docs.sheetjs.com/knex/SheetJSKnexTest.js

This script will:

• read and parse the test file pres.numbers
• create a connection to a SQLite database stored at SheetJSKnex.db
• load data from the first worksheet into a table with name Test_Table
• disconnect and reconnect to the database
• dump data from the table Test_Table
• export the dataset to SheetJSKnex.xlsx

4. Run the script:

node SheetJSKnexTest.js

The script will generate two artifacts:

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

npx xlsx-cli SheetJSKnex.xlsx

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

sqlite3 SheetJSKnex.db 'select * from Test_Table'

---

1. See select in the KnexJS query builder documentation. ↩︎

2. See json_to_sheet in "Utilities" ↩︎

3. See "Sheet Objects" in "SheetJS Data Model" for more details. ↩︎

4. See "Workbook Helpers" in "Utilities" for details on book_new and book_append_sheet. ↩︎

5. See writeFile in "Writing Files" ↩︎

6. See sheet_to_json in "Utilities" ↩︎

7. See insert in the KnexJS query builder documentation. ↩︎

8. See createTable in the KnexJS Schema Builder documentation. ↩︎

9. See dropTableIfExists in the KnexJS Schema Builder documentation. ↩︎