7.2 KiB
| title |
|---|
| NoSQL Data Stores |
import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';
So-called "Schema-less" databases allow for arbitrary keys and values within the entries in the database. K/V stores and Objects add additional restrictions.
:::note
These data stores are capable of storing structured data. Those use cases are covered in the Database demo.
:::
Arbitrary Data to Spreadsheets
There is no natural way to translate arbitrarily shaped schemas to worksheets in a workbook. One common trick is to dedicate one worksheet to holding named keys. For example, considering the JS object:
{
"title": "SheetDB",
"metadata": {
"author": "SheetJS",
"code": 7262
},
"data": [
{ "Name": "Barack Obama", "Index": 44 },
{ "Name": "Donald Trump", "Index": 45 },
]
}
A dedicated worksheet should store the one-off named values:
XXX| A | B |
---+-----------------+---------+
1 | Path | Value |
2 | title | SheetDB |
3 | metadata.author | SheetJS |
4 | metadata.code | 7262 |
Data Stores
Redis
Redis has 5 core data types: "String", List", "Set", "Sorted Set", and "Hash". Since the keys and values are limited to simple strings (and numbers), it is possible to store complete databases in a single worksheet.
Mapping
The first row holds the data type and the second row holds the property name.
Strings can be stored in a unified String table. The first column holds keys and the second column holds values:
XXX| A | B |
---+---------+-------+
1 | Strings | |
2 | | |
3 | Hello | World |
4 | Sheet | JS |
The SheetJS array-of-arrays representation of the string table is an array of key/value pairs:
let aoa = ["Strings"]; aoa.length = 2; // [ "Strings", empty ]
const keys = await client.KEYS("*");
for(let key of keys) {
const type = await client.TYPE(key);
if(type == "string") aoa.push([key, await client.GET(key)]);
}
Lists are unidimensional and can be stored in their own columns.
XXX| C |
---+---------+
1 | List |
2 | List1 |
3 | List1V1 |
4 | List1V2 |
The SheetJS array-of-arrays representation of lists is a column of values.
if(type == "list") {
let values = await client.LRANGE(key, 0, -1);
aoa = [ ["List"], [key] ].concat(values.map(v => [v]));
}
Sets are unidimensional and can be stored in their own columns.
XXX| D |
---+-------+
1 | Set |
2 | Set1 |
3 | Set1A |
4 | Set1B |
The SheetJS array-of-arrays representation of sets is a column of values.
if(type == "set") {
let values = await client.SMEMBERS(key);
aoa = [ ["Set"], [key] ].concat(values.map(v => [v]));
}
Sorted Sets have an associated score which can be stored in the second column.
XXX| E | F |
---+---------+---+
1 | Sorted | |
2 | ZSet1 | |
3 | Key1 | 1 |
4 | Key2 | 2 |
The SheetJS array-of-arrays representation is an array of key/score pairs.
if(type == "zset") {
let values = await client.ZRANGE_WITHSCORES(key, 0, -1);
aoa = [ ["Sorted"], [key] ].concat(values.map(v => [v.value, v.score]));
}
Hashes are stored like the string table, with key and value columns in order.
XXX| G | H |
---+-------+-------+
1 | Hash | |
2 | Hash1 | |
3 | Key1 | Val1 |
4 | Key2 | Val2 |
The SheetJS array-of-arrays representation is an array of key/value pairs.
if(type == "hash") {
let values = await client.HGETALL(key);
aoa = [ ["Hash"], [key] ].concat(Object.entries(values));
}
Example
Complete Example (click to show)
-
Set up and start a local Redis server
-
Download the following scripts:
- Install dependencies and run:
npm i --save https://cdn.sheetjs.com/xlsx-latest/xlsx-latest.tgz redis
node SheetJSRedisTest.mjs
Inspect the output and compare with the data in SheetJSRedisTest.mjs.
Open SheetJSRedis.xlsx and verify the columns have the correct data
PouchDB
Database#allDocs is the standard approach for bulk data export. The generated
row objects have additional _id and _rev keys that should be removed.
Nested objects must be flattened. The "Tutorial" includes an example of constructing a simple array.
function export_pouchdb_to_xlsx(db) {
/* fetch all rows, including the underlying data */
db.allDocs({include_docs: true}, function(err, doc) {
/* pull the individual data rows */
const aoo = doc.rows.map(r => {
/* `rest` will include every field from `r` except for _id and _rev */
const { _id, _rev, ...rest } = r;
return rest;
});
/* generate worksheet */
const ws = XLSX.utils.json_to_sheet(aoo);
/* generate workbook and export */
const wb = XLSX.utils.book_new();
XLSX.utils.book_append_sheet(wb, ws, "Sheet1");
XLSX.writeFile(wb, "SheetJSPouch.xlsx");
});
}
Complete Example (click to show)
- Download the "Working Version" from the Getting Started guide.
The ZIP file should have MD5 checksum ac4da7cb0cade1be293ba222462f109c:
curl -LO https://github.com/nickcolley/getting-started-todo/archive/master.zip
md5sum master.zip || md5 master.zip
### the checksum will be printed
If the download is unavailable, a mirror is available at https://docs.sheetjs.com/pouchdb/master.zip
- Unzip the
master.zipfile and enter the folder:
unzip master.zip
cd getting-started-todo-master
- Edit
index.htmlto reference the SheetJS library and add a button:
<body>
<!-- highlight-start -->
<script src="https://cdn.sheetjs.com/xlsx-latest/package/dist/xlsx.full.min.js"></script>
<button id="xport">Export!</button>
<!-- highlight-end -->
<section id="todoapp">
- Just before the end of
app.js, add aclickevent listener:
if (remoteCouch) {
sync();
}
// highlight-start
document.getElementById("xport").addEventListener("click", function() {
db.allDocs({include_docs: true}, function(err, doc) {
const aoo = doc.rows.map(r => {
const { _id, _rev, ... rest } = r.doc;
return rest;
});
const ws = XLSX.utils.json_to_sheet(aoo);
const wb = XLSX.utils.book_new(); XLSX.utils.book_append_sheet(wb, ws, "Sheet1");
XLSX.writeFile(wb, "SheetJSPouch.xlsx");
});
});
// highlight-end
})();
- Start a local web server:
npx http-server .
Access http://localhost:8080 from your browser. Add a few items and click
the "Export!" button to generate a new file.