Scalar types (String, Int, Float, Boolean, ID) in GraphQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a String scalar type in GraphQL?

A String scalar type represents textual data. It is used to store sequences of characters like names, descriptions, or any text.

beginner

What kind of values does the Int scalar type hold in GraphQL?

The Int scalar type holds whole numbers without decimals, like 1, 42, or -7. It is used for counting or indexing.

beginner

Explain the Float scalar type in GraphQL.

The Float scalar type stores numbers with decimals, such as 3.14 or -0.001. It is used for precise measurements or calculations.

beginner

What does the Boolean scalar type represent in GraphQL?

The Boolean scalar type represents true or false values. It is used for yes/no or on/off conditions.

beginner

What is the purpose of the ID scalar type in GraphQL?

The ID scalar type is a unique identifier, often used to identify objects. It is serialized as a string but treated specially to represent unique keys.

Which scalar type would you use to store a user's age?

A Boolean

B String

C Float

D Int

Age is a whole number, so the Int scalar type is the best choice.

Which scalar type is best for storing a product price like 19.99?

A Int

B Boolean

C Float

D ID

Float is used for numbers with decimals, like prices.

What scalar type would you use to represent a true/false value?

A ID

B Boolean

C String

D Float

Boolean stores true or false values.

Which scalar type is typically used for unique object identifiers?

A ID

B Int

C String

D Boolean

ID is used for unique identifiers, often serialized as strings.

If you want to store a person's full name, which scalar type should you choose?

A String

B Int

C Float

D Boolean

String is used for text like names.

Describe the five main scalar types in GraphQL and give a simple example for each.

Think about common data types you use in everyday life.

Explain why the ID scalar type is different from a String even though it is serialized as a string.

Consider how IDs help find specific items in a list.

Practice

1. Which of the following is NOT a standard GraphQL scalar type?

easy

A. Boolean

B. String

C. Date

D. ID

Solution

1. Step 1: Recall standard GraphQL scalar types

   The standard scalar types are String, Int, Float, Boolean, and ID.

2. Step 2: Identify the non-standard type

   Date is not a built-in scalar type in GraphQL; it requires a custom scalar.

3. Final Answer:

   Date -> Option C

4. Quick Check:

   Standard scalars exclude Date [OK]

Hint: Remember only 5 built-in scalars: String, Int, Float, Boolean, ID [OK]

Common Mistakes:

• Thinking Date is built-in
• Confusing ID with Int
• Assuming Boolean is custom

2. Which of the following is the correct way to declare a field of type ID in a GraphQL schema?

easy

A. userId: id

B. userId: Int

C. userId: String!

D. userId: ID!

Solution

1. Step 1: Understand GraphQL type syntax

   Types are case-sensitive; ID must be uppercase and non-null indicated by !.

2. Step 2: Check each option

   userId: ID! uses correct type 'ID!' with uppercase and non-null. Others are either lowercase or wrong type.

3. Final Answer:

   userId: ID! -> Option D

4. Quick Check:

   ID type is uppercase and non-null with ! [OK]

Hint: ID type is uppercase and ! means non-null [OK]

Common Mistakes:

• Using lowercase 'id'
• Confusing ID with String
• Omitting ! for required fields

3. Given this GraphQL query result for a field declared as Float:
{ price: 19 }
What is the actual type of the returned value?

medium

A. Float

B. String

C. Integer

D. Boolean

Solution

1. Step 1: Understand GraphQL Float type

   Float represents decimal numbers but can also return whole numbers as floats.

2. Step 2: Analyze the value 19

   Even though 19 looks like an integer, GraphQL returns it as a Float type because the field is Float.

3. Final Answer:

   Float -> Option A

4. Quick Check:

   Float fields return numbers as floats, even whole numbers [OK]

Hint: Float fields always return float type, even if whole number [OK]

Common Mistakes:

• Assuming 19 is Integer
• Thinking Float must have decimal point
• Confusing with String

4. Identify the error in this GraphQL schema snippet:

type Product {
  id: ID
  name: String!
  price: float
  inStock: Boolean
}

medium

A. 'Boolean' should be lowercase 'boolean'

B. 'float' should be 'Float' with uppercase F

C. 'ID' should be 'Id' with lowercase d

D. 'String!' should be 'String' without exclamation mark

Solution

1. Step 1: Check scalar type capitalization

   GraphQL scalar types are case-sensitive; 'Float' must be capitalized.

2. Step 2: Verify other types

   'Boolean' and 'ID' are correctly capitalized; 'String!' is valid for non-null.

3. Final Answer:

   'float' should be 'Float' with uppercase F -> Option B

4. Quick Check:

   Scalar types must be capitalized exactly [OK]

Hint: Scalar types always start with uppercase letter [OK]

Common Mistakes:

• Using lowercase scalar types
• Changing Boolean case
• Removing ! from non-null

5. You want to store a unique identifier for users that is a string but should never be null. Which scalar type and modifier combination is best in GraphQL schema?

hard

A. ID!

B. String

C. Int!

D. Boolean!

Solution

1. Step 1: Understand the purpose of ID scalar

   ID is designed for unique identifiers and is serialized as string.

2. Step 2: Ensure non-null constraint

   Adding ! means the field cannot be null, which fits the requirement.

3. Final Answer:

   ID! -> Option A

4. Quick Check:

   Use ID! for unique, non-null string identifiers [OK]

Hint: Use ID! for unique, required string IDs [OK]

Common Mistakes:

• Using String without !
• Using Int for string IDs
• Using Boolean for IDs