Get all the column names in a table in MongoDB

In MongoDB, there is no concept of columns since MongoDB is schema-less and does not contain tables. It contains the concept of collections and a collection has different types of documents with varying field structures.

Syntax

// Insert documents with different field structures
db.collectionName.insertOne({"fieldName1": "value1", "fieldName2": "value2"});

// Get all field names from a single document
db.collectionName.findOne();

// Get all documents to see different field structures
db.collectionName.find();

Sample Data

Let us create a collection with documents having different field structures ?

db.collectionOnDifferentDocumentDemo.insertMany([
    {"UserName": "Larry"},
    {"UserName": "David", "UserAge": 24},
    {"UserName": "Carol", "UserAge": 25, "UserCountryName": "US"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c953b98749816a0ce933682"),
        ObjectId("5c953ba4749816a0ce933683"),
        ObjectId("5c953bb8749816a0ce933684")
    ]
}

Method 1: Get All Field Names Using find()

Display all documents to see the different field structures across the collection ?

db.collectionOnDifferentDocumentDemo.find();

{ "_id": ObjectId("5c953b98749816a0ce933682"), "UserName": "Larry" }
{ "_id": ObjectId("5c953ba4749816a0ce933683"), "UserName": "David", "UserAge": 24 }
{ "_id": ObjectId("5c953bb8749816a0ce933684"), "UserName": "Carol", "UserAge": 25, "UserCountryName": "US" }

Method 2: Get Field Names from Single Document

Use findOne() to see the field structure of the first document ?

db.collectionOnDifferentDocumentDemo.findOne();

{ "_id": ObjectId("5c953b98749816a0ce933682"), "UserName": "Larry" }

Key Points

• MongoDB collections can have documents with different field structures.
• Use find() to see all field variations across documents.
• Use findOne() to examine a single document's field structure.

Conclusion

MongoDB's schema-less nature allows documents in the same collection to have different fields. Use find() or findOne() to explore the field structures present in your collection documents.