website/content/blog/simple-kv-store-sqlite.md
2024-09-17 16:49:52 -04:00

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---
title: "Simple Key-Value Store using Sqlite3"
date: 2023-11-09T22:15:23-05:00
draft: false
tags: ["DB"]
math: false
medium_enabled: false
---
A lot of software nowadays are built for scale. You have to setup a Kubernetes cluster and deploy Redis for duplication in order to have a key-value store. Though for many small projects, I feel like it's overkill.
I'll show in this post, that we can have a nice simple[^1] key-value store using `sqlite3`. This gives us the benefit that we don't need to use system resources to run a daemon the entire time and only spin up a process when we need it.
For our key-value store, we're going to use a table with two columns:
- A key, which we'll call `name`. This will be a unique `TEXT` type that has to be set.
- The value, which we'll call `value` (Creative, I know.) For our purposes, this will also be a `TEXT` type.
The SQL to create this table is[^2]
```sql
CREATE TABLE config(
name TEXT PRIMARY KEY,
value TEXT
);
```
Let's say we want to get the value of the key `author`. This is a `SELECT` statement away:
```sql
SELECT value FROM config where name='author';
```
Now let's say that we want to insert a new key into the table.
```sql
INSERT INTO config(name, value) VALUES ('a', '1');
```
What about updating?
```sql
UPDATE config SET value='2' WHERE name='a';
```
The tricky part is if we want to insert if the key does not exist, and update if it does. To handle this we'll need to resolve the [conflict](https://www.sqlite.org/lang_conflict.html).
```sql
INSERT INTO config(name, value) VALUES ('a', '3') ON CONFLICT(name) DO UPDATE SET value=excluded.value;
```
Lastly if you want to export the entire key-value store as a CSV:
```bash
sqlite3 -header -csv data.db "SELECT * FROM config;"
```
This is nice and all, but it's inconvinient to type out all these SQL commands. Therefore, I wrote two little bash scripts.
**`sqlite3_getkv`**
```bash
#!/bin/sh
set -o errexit
set -o nounset
set -o pipefail
show_usage() {
echo "Usage: sqlite3_getkv [db_file] [key]"
exit 1
}
# Check argument count
if [ "$#" -ne 2 ]; then
show_usage
fi
# Initalize database file is not already
sqlite3 "$1" "CREATE TABLE IF NOT EXISTS config(name TEXT NOT NULL UNIQUE, value TEXT);"
# Get value from key
sqlite3 "$1" "SELECT value FROM CONFIG where name='$2';"
```
**`ssqlite3_setkv`**
```bash
#!/bin/sh
set -o errexit
set -o nounset
set -o pipefail
show_usage() {
echo "Usage: sqlite3_setkv [db_file] [key] [value]"
exit 1
}
# Check argument count
if [ "$#" -ne 3 ]; then
show_usage
fi
# Initalize database file is not already
sqlite3 "$1" "CREATE TABLE IF NOT EXISTS config(name TEXT NOT NULL UNIQUE, value TEXT);"
# Set key-value pair
sqlite3 "$1" "INSERT INTO config(name, value) VALUES ('$2', '$3') ON CONFLICT(name) DO UPDATE SET value=excluded.value;"
```
**Example Usage:**
```
$ ./sqlite3_setkv.sh test.db a 4
$ ./sqlite3_setkv.sh test.db c 5
$ ./sqlite3_getkv.sh test.db a
4
$ ./sqlite3_setkv.sh test.db a 5
$ ./sqlite3_getkv.sh test.db a
5
```
[^1]: Somehow my idea of easier, simpler, and more maintainable is writing bash scripts.
[^2]: Thanks Justin for helping me simplify it from `NOT NULL UNIQUE` to `PRIMARY KEY`.