MongoDB to Couchbase (Part 3): Data Types

MongoDB

Couchbase

Data types

https://docs.mongodb.com/manual/reference/bson-types/

Data types

https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/datatypes.html

Stored in BSON format. BSON is MongoDB’s extended and binary representation for JSON.  It follows the JSON model, but adds types like Double, Date, timestamp, code, and some internal types. Here’s we’ll only discuss the types directly used by the application. 

Stored in JSON format. Physical storage compresses the JSON using snappy compression. 

BASIC TYPES

Double

{salary: 88345.4299 }

Number

{“salary”: 88345.4299 }

Int64/Int32

64-bit and 32-bit signed integer.

Number

Numbers can be stored in integer, decimal, floating point and scientific notation. 

Decimal

MongoDB supports IEEE 754 decimal128 data type and provides various operators to convert to and from its decimal data type. 

Insert as: 

{"price" : NumberDecimal("2.098")}

Shows as:

{price: Decimal128(“2.098”)}

Does not support decimal data type.  You can store the decimals as JSON numerical value, but perform the arithmetic in the application before storing it so you get the exact scale and precision. E.g. You can use the BigDecmial in Java. 

{"price" : 2.098 }

String

UTF-8 encoded string

{“company”: “MongoDB”}

String

This is same as MongoDB. String in JSON is of UTF-8 encoding.

{“company”: “Couchbase”}

Date

Uses ISO8601 form and provides special function in Mongo shell to encode it and it’s encoded in the BSON date format.

Insert as:

{created: ISODate("2012-12-19T06:01:17.171Z")}

Shows up as:

{created: ISODate("2012-12-19T06:01:17.171Z")}

Date as a special data type is unavailable. The best practice is to store the data as a string in ISO8601 format and use the rich set of functions to extract, manipulate and do arithmetic on the data value. All of the common functionality on date is supported.

{“created”: "2012-12-19T06:01:17.171Z"}

Timestamp is simply epoch time in milliseconds. It’s usually used to store elapsed time in Jan 1st 1970.

{"$timestamp":{"t":1565545664,"i":1}}

Timestamp isn’t supported directly, a rich set of functions can convert milliseconds since Jan 1st, 1970 to other formats and vice versa.  On the JSON document, it’s simply stored as an unsigned numeric value. 

ObjectID

Every document in MongoDB is identified by either user generated or system generated id. When user does not specify a value for the _id field, the system generated an objectID automatically for the document.  This value is stored within the document and an index is automatically created on this field. User does not have an option to drop it. 

{_id: ObjectId("622d7fbe57fe91991b9340f5")}

Document Key

Each couchbase document must have a user-generated document key string that’s unique per collection. If you don’t care about the structure of the document key, you can simply generate the key using a UUID() or equivalent function. The uniqueness is enforced during insert and cannot be changed. The document key resides outside the document. The document can be accessed directly via API or N1QL if you know the document key. 

INSERT INTO t(KEY, VALUE) VALUES(“cx:123:PR”, {“a”:1, “b”:55});

INSERT INTO t(KEY, VALUE) VALUES(UUID(), {“a”:1, “b”:55});

NULL

These are known unknowns. This is a field defined within the document but with an unknown value.

{“address”: null}

NULL

This is defined by JSON and means the same thing as MongoDB.

{“address”: null}

No definition of missing.

MISSING

Since JSON is a flexible schema, querying a field not present in the document won’t give an error.  But, you can inspect to see if the field has an unknown value or the field itself is missing by using the IS MISSING predicate. 

To account for MISSING, Couchbase has defined the 4-valued boolean logic.

COMPLEX TYPES

OBJECT type

JSON (and BSON) as a whole represents an object and is an object. These objects can contain other objects.  Nesting of other objects is a basic property. 

{

  _id: "SF:QB:13",

  team: "49ers",

  name: {

    first: "joe",

    last: "montana",

    superbowls: [

      1982,

      1985,

      1989,

      1990

    ]

  }

}

OBJECT type

This is the same as MongoDB. A JSON document itself is an object. You can nest an object within another object. You can have an object of scalars, objects of objects, objects of arrays, objects of arrays of objects. This ability to nest objects without pre-planning while creating a collection gives the Couchbase and MongoDB collections the “flexible schema” ability. 

Document key:  "SF:QB:13"

{

  team: "49ers",

  "name": {

    "first": "joe",

    "last": "montana",

    "superbowls": [

      1982,

      1985,

      1989,

      1990

    ]

  }

}

ARRAY

Array is more of a data structure than a data type.  An array can contain zero, one or more values of any type: string, double, object, etc. Arrays can contain other arrays forming n-dimensional matrix. Array type makes the document model truly flexible, extensible. It also is a challenge to query, index and meet the demanding SLAs.

{mytoys: []}

{mytoys: [“lego”, “cp360”, 4842, 85]}

{mytoys: [[1, 2], [“a”, “y”, “b], [42, “xyz”]}

{mytoys: {x: [1, 5, 2, 4]}}

{mytoys: [{a:1, b:2}, {a:8, c:43}, {a:”x”, b:23}]

ARRAY

Arrays in MongoDB and standard JSON are exactly the same. Couchbase provides more advanced indexing and optimization features for arrays – this will be discussed later in the series. 

{“mytoys”: []}

{“mytoys”: [“lego”, “cp360”, 4842, 85]}

{“mytoys”: [[1, 2], [“a”, “y”, “b”], [42, “xyz”]}

{“mytoys”: {“x”: [1, 5, 2, 4]}}

{“mytoys”: [{“a”:1, “b”:2}, {“a”:8, “c”:43}, {“a”:”x”, “b”:23}]

TYPE RELATED FEATURES

Type comparison and sort order

Null has the lowest value and Timestamp has the highest value. In order: Null, Numbers, String, Object, Array, BinData, ObjectId, Boolean, Timestamp, RegularExpression. 

Type comparison and sort order (collation)

MISSING has the lowest values and Object has the highest value within the types. When comparing documents. In order, MISSING, NULL, FALSE, TRUE, number, string, array, object