Deno KV (built-in key-value store) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Deno KV?

Deno KV is a built-in key-value store in Deno that lets you save and retrieve data quickly using simple keys and values.

beginner

How do you open a connection to Deno KV?

You open a connection by calling await Deno.openKv(). This gives you access to the key-value store.

beginner

How do you store a value in Deno KV?

Use kv.set(key, value) where key is an array of strings or numbers and value is the data you want to save.

beginner

How do you retrieve a value from Deno KV?

Use kv.get(key) with the same key you used to store the value. It returns an object with a value property containing the saved value or null if not found.

intermediate

What is the format of keys in Deno KV?

Keys are arrays of strings or numbers, like ["user", "123"]. This lets you organize data in a simple hierarchy.

Which method opens the Deno KV store?

A await Deno.openKv()

B Deno.connectKv()

C Deno.startKv()

D Deno.initKv()

You open the key-value store with await Deno.openKv().

How do you save data in Deno KV?

A kv.save(key, value)

B kv.store(key, value)

C kv.put(key, value)

D kv.set(key, value)

The correct method to save data is kv.set(key, value).

What type of data structure is used for keys in Deno KV?

A String only

B Number only

C Array of strings or numbers

D Object with key-value pairs

Keys are arrays of strings or numbers, like ["user", "123"].

What does kv.get(key) return if the key does not exist?

A Throws an error

B Returns null

C Returns undefined

D Returns an empty string

kv.get(key) returns null if the key is not found.

Which of these is a valid key for Deno KV?

A ["user", 123]

B "user123"

C {user: 123}

D 12345

Keys must be arrays of strings or numbers, like ["user", 123].

Explain how to store and retrieve data using Deno KV.

Think about opening the store first, then saving and getting data with keys.

Describe the key format in Deno KV and why it is useful.

Imagine keys like folders and subfolders to organize files.

Practice

1. What is the correct way to store a value in Deno KV?

easy

A. Use kv.set(["key"], value) to save data.

B. Use kv.save("key", value) to save data.

C. Use kv.put("key", value) to save data.

D. Use kv.store(["key"], value) to save data.

Solution

1. Step 1: Understand Deno KV key format

   Deno KV uses arrays as keys, so keys must be passed as arrays like ["key"].

2. Step 2: Identify the correct method to save data

   The method to save data is set, so kv.set(["key"], value) is correct.

3. Final Answer:

   Use kv.set(["key"], value) to save data. -> Option A

4. Quick Check:

   Key as array + set method = Use kv.set(["key"], value) to save data. [OK]

Hint: Remember: keys are arrays and method is set [OK]

Common Mistakes:

• Using string keys instead of array keys
• Using wrong method names like save or put
• Passing key as a single string instead of array

2. Which of the following is the correct syntax to read a value from Deno KV?

easy

A. const result = kv.get(["key"]);

B. const result = await kv.get("key");

C. const result = await kv.get(["key"]);

D. const result = kv.get("key");

Solution

1. Step 1: Recognize key format for get method

   Deno KV requires keys as arrays, so the key must be passed as ["key"].

2. Step 2: Confirm asynchronous usage of get

   The get method is asynchronous, so it must be awaited.

3. Final Answer:

   const result = await kv.get(["key"]); -> Option C

4. Quick Check:

   Await + array key + get method = const result = await kv.get(["key"]); [OK]

Hint: Always await get and use array keys [OK]

Common Mistakes:

• Not awaiting the get method
• Passing key as string instead of array
• Using synchronous call without await

3. What will be the output of this code snippet?

const kv = await Deno.openKv();
await kv.set(["user", "name"], "Alice");
const result = await kv.get(["user", "name"]);
console.log(result.value);

medium

A. undefined

B. "Alice"

C. null

D. Throws an error

Solution

1. Step 1: Store value with key ["user", "name"]

   The code stores the string "Alice" under the key array ["user", "name"].

2. Step 2: Retrieve the stored value using the same key

   The get method fetches the stored value, which is "Alice".

3. Final Answer:

   "Alice" -> Option B

4. Quick Check:

   Set then get with same key returns stored value [OK]

Hint: Set then get with same key returns stored value [OK]

Common Mistakes:

• Expecting key as string instead of array
• Not awaiting async calls
• Confusing result object with direct value

4. Identify the error in this Deno KV usage:

const kv = await Deno.openKv();
await kv.set("session", "active");
const status = await kv.get(["session"]);
console.log(status.value);

medium

A. The key in set should be an array, not a string.

B. The get method should not be awaited.

C. The value "active" must be an object, not a string.

D. The console.log should print status directly, not status.value.

Solution

1. Step 1: Check key format in set method

   The set method requires the key to be an array, but here it is a string "session".

2. Step 2: Confirm correct key format for get method

   The get method uses the key as an array ["session"], which is correct.

3. Final Answer:

   The key in set should be an array, not a string. -> Option A

4. Quick Check:

   Key must be array in set and get [OK]

Hint: Keys must always be arrays in set and get [OK]

Common Mistakes:

• Using string keys instead of array keys
• Not awaiting async methods
• Misunderstanding value access from get result

5. You want to store user preferences with keys like ["user", userId, "prefs"] and values as objects. Which code correctly updates preferences for userId 42 without overwriting other keys?

const kv = await Deno.openKv();
const userId = 42;
const newPrefs = { theme: "dark" };
// Which code below is correct?

hard

A. await kv.set([userId, "prefs"], newPrefs);

B. await kv.set(["user", "prefs"], newPrefs);

C. await kv.set(["user", userId], newPrefs);

D. await kv.set(["user", userId, "prefs"], newPrefs);

Solution

1. Step 1: Understand key structure for user preferences

   The key must include "user", the userId, and "prefs" to uniquely identify preferences per user.

2. Step 2: Check which option uses the full key correctly

   await kv.set(["user", userId, "prefs"], newPrefs); uses ["user", userId, "prefs"] which matches the required key structure.

3. Final Answer:

   await kv.set(["user", userId, "prefs"], newPrefs); -> Option D

4. Quick Check:

   Full key array with userId keeps keys unique [OK]

Hint: Include userId in key array to avoid overwriting [OK]

Common Mistakes:

• Omitting userId from key causing overwrites
• Using incomplete key arrays
• Confusing order of key elements