Nested JSON Flattening

The Flattening Challenge

One of the biggest challenges in data format conversion is handling nested JSON structures. APIs often return deeply nested objects and arrays, but CSV and Excel require flat, tabular data. This guide covers proven strategies for flattening complex JSON while preserving data integrity.

Strategy 1: Dot Notation Flattening

Transform nested object paths into flat column names using dot notation.

Example

{
  "id": 1,
  "user": {
    "name": "Alice",
    "contact": {
      "email": "alice@ex.com",
      "phone": "555-0100"
    }
  }
}

id,user.name,user.contact.email,user.contact.phone
1,Alice,alice@ex.com,555-0100

Pros & Cons

Strategy 2: Array Expansion

Create multiple rows for array items, duplicating parent data in each row.

Example

{
  "orderId": "A123",
  "customer": "Alice",
  "items": [
    {"product": "Laptop", "qty": 1},
    {"product": "Mouse", "qty": 2}
  ]
}

orderId,customer,product,qty
A123,Alice,Laptop,1
A123,Alice,Mouse,2

Pros & Cons

Strategy 3: JSON String Preservation

Keep complex nested structures as JSON strings within CSV cells.

Example

{
  "id": 1,
  "name": "Alice",
  "metadata": {
    "tags": ["vip", "priority"],
    "preferences": {
      "theme": "dark",
      "locale": "en-US"
    }
  }
}

id,name,metadata
1,Alice,"{""tags"":[""vip"",""priority""],""preferences"":{""theme"":""dark"",""locale"":""en-US""}}"

Pros & Cons

Strategy 4: Multiple Tables (Relational)

Split into related tables with foreign keys, like a relational database.

Example

{
  "orderId": "A123",
  "customer": "Alice",
  "items": [
    {"product": "Laptop", "price": 999},
    {"product": "Mouse", "price": 25}
  ]
}

orderId,customer
A123,Alice

orderId,product,price
A123,Laptop,999
A123,Mouse,25

Pros & Cons

Choosing the Right Strategy

Handling Deep Nesting (5+ Levels)

Practical Tips

• 1.
  Know Your Audience: Excel users prefer expanded rows, developers prefer dot notation
• 2.
  Test with Real Data: Edge cases often appear only with production data
• 3.
  Document Your Approach: Future you will thank present you
• 4.
  Consider Round-Trip: Can you convert back to original JSON if needed?