Introduction

A separate database plugin to support MongoDB-specific features and configurations.

Use-Case

Users can choose and install MongoDB source and sink plugins.
Users should see MongoDB logo on plugin configuration page for better experience.
Users should get relevant information from the tool tip:
- The tool tip should describe accurately what each field is used for.
Users should not have to specify any redundant configuration
Users should get field level lineage for the source and sink that is being used.
Reference documentation should be updated to account for the changes.
The source code for MongoDB database plugin should be placed in repo under data-integrations org.
The data pipeline using source and sink plugins should run on both mapreduce and spark engines.

User Stories

User should be able to install MongoDB specific database source and sink plugins from the Hub
Users should have each tool tip accurately describe what each field does
Users should get field level lineage information for the MongoDB source and sink
Users should be able to setup a pipeline avoiding specifying redundant information
Users should get updated reference document for MongoDB source and sink
Users should be able to read all the DB types

Plugin Type

Design Tips

MongoDB driver reference: http://mongodb.github.io/mongo-java-driver/3.10/driver/

Design

The suggestion is to move existing mongodb-plugins module to the mongodb-plugins repository.

MongoDB Overview

Document database

A record in MongoDB is a document, which is a data structure composed of field and value pairs. MongoDB documents are similar to JSON objects. The values of fields may include other documents, arrays, and arrays of documents.

{
    "_id" : ObjectId("5d3f1c2a2f547625b0bbb397"),
    "string" : "AAPL",
    "int32" : 10,
    "double" : 23.23,
    "array" : [ 
        "a1", 
        "a2"
    ],
    "object" : {
        "inner_field" : "val"
    },
    "binary" : { "$binary" : "YmluYXJ5IGRhdGE=", "$type" : "00" },
    "undefined" : undefined,
    "boolean" : false,
    "date" : ISODate("2019-07-29T16:17:46.109Z"),
    "null" : null,
    "regex" : /./,
    "dbpointer" : DBRef("source", "5d079ee6d078c94008e4bb3a"),
    "javascript" : var l = 1;,
    "javascriptwithscope" : { "$code" : var l = 1; ,  "$scope" : { "scope" : "scope_val" } },
    "symbol" : "a",
    "timestamp" : Timestamp(1564417066, 1),
    "long" : NumberLong(9223372036854775807),
    "decimal" : NumberDecimal("3.100000"),
    "minkey" : { "$minKey" : 1 },
    "maxkey" : { "$maxKey" : 1 }
}

BSON

BSON is a binary serialization format used to store documents and make remote procedure calls in MongoDB. The BSON specification is located at bsonspec.org

Document limitations

The maximum BSON document size is 16 megabytes.
In MongoDB, each document stored in a collection requires a unique _id field that acts as a primary key. If an inserted document omits the _id field, the MongoDB driver automatically generates an ObjectId for the _id field.

Flexible schema

Unlike SQL databases, where you must determine and declare a table’s schema before inserting data, MongoDB’s collections, by default, does not require its documents to have the same schema.

The documents in a single collection do not need to have the same set of fields and the data type for a field can differ across documents within a collection.
To change the structure of the documents in a collection, such as add new fields, remove existing fields, or change the field values to a new type, update the documents to the new structure.

Query filter documents

A query filter document and query operators can be used to specify conditions.

The following example uses '{ status: { $in: [ "A", "D" ] } }' query filter document to retrieve all documents from the 'inventory' collection where 'status' equals either "A" or "D":

db.inventory.find( { status: { $in: [ "A", "D" ] } } )

The operation corresponds to the following SQL statement:

SELECT * FROM inventory WHERE status in ("A", "D")

Sink Properties

User Facing Name	Widget Type	Description	Constraints

User Facing Name	Widget Type	Description	Constraints
Label	textbox	Label for UI.
Reference Name	textbox	Uniquely identified name for lineage.
Host	textbox	Host that MongoDB is running on.	Required (defaults to localhost on UI)
Port	number	Port that MongoDB is listening to.	Optional (default 27017)
Database	textbox	MongoDB database name.	Required
Collection	textbox	Name of the database collection to write to.	Required
ID Field	textbox	Allows the user to specify which of the incoming fields should be used as an object identifier.	Optional. Object ID will be generated if no value is specified.
Username	textbox	User identity for connecting to the specified database.
Password	password	Password to use to connect to the specified database.
Connection Arguments	keyvalue	A list of arbitrary string key/value pairs as connection arguments. See Connection String Options for a full description of these arguments.

Sink Data Types Mapping

To support all data types in the Sink we can use MongoDB extended JSON format or/and infer a data type of record field based on its name.

The table below does not honor non-standard MongoDB data types and lists how CDAP data types are stored.

The following MongoDB data types are missing: Undefined, Regular Expression, DBPointer, JavaScript, Symbol, JavaScript (with scope), Timestamp, Min key, Max key.

CDAP Schema Data Type	MongoDB Data Types	Comment

CDAP Schema Data Type	MongoDB Data Types	Comment
boolean	Boolean
bytes	Binary data, ObjectId(if 'ID Field' specified)
date	Date
double	Double
decimal	Decimal128	The Decimal128 type supports up to 34 digits of precision.
float	Double
int	32-bit integer
long	64-bit integer
string	String, ObjectId(if 'ID Field' specified)
time	String
timestamp	Date
array	Array
record	Object
enum	String
map	Object
union	Depends on the actual value. For example, if it's a union: `["string","int","long"]` and the value is actually a long, the mongo document will have the field as a 64-bit integer. If a different record comes in with the value as a string, the mongo document will end up with a String for that field.

Source Properties

User Facing Name	Widget Type	Description	Constraints

User Facing Name	Widget Type	Description	Constraints
Label	textbox	Label for UI.
Reference Name	textbox	Uniquely identified name for lineage.
Host	textbox	Host that MongoDB is running on.	Required (defaults to localhost on UI)
Port	number	Port that MongoDB is listening to.	Optional (default 27017)
Database	textbox	MongoDB database name.	Required
Collection	textbox	Name of the database collection to write to.	Required
Output Schema	schema	Specifies the schema of the documents.	Required
On Record Error	radio-group	Specifies how to handle error in record processing. An error will be thrown if failed to parse value according to a provided schema.	Possible values are: Skip error Fail pipeline Default: 'Fail pipeline'
Input Query	json-editor	Optionally filter the input collection with a query. This query must be represented in JSON format and use the MongoDB extended JSON format to represent non-native JSON data types.
Username	textbox	User identity for connecting to the specified database.
Password	password	Password to use to connect to the specified database.
Authentication Connection String	textbox	Auxiliary MongoDB connection string to authenticate against when constructing splits.
Connection Arguments	keyvalue	A list of arbitrary string key/value pairs as connection arguments. See Connection String Options for a full description of these arguments.

Source Data Types Mapping

The source requires Output Schema to be set. Based on the schema source will expect a field in each document to be of a specific Mongo data type.

On Record Error error handling property allows the user to decide whether the pipeline should fail, the record should be skipped, or the record should be sent to the error dataset.

The following table shows what MongoDB data types can be read as CDAP types.

CDAP Schema Data Type	MongoDB Data Types

CDAP Schema Data Type	MongoDB Data Types
boolean	Boolean
bytes	Binary data, ObjectId
date	-
double	Double
decimal	Decimal128
float	-
int	32-bit integer
long	64-bit integer
string	String, Symbol
time	-
timestamp	Date
array	Array
record	Object The following schema: `{"type":"record","name":"object","fields":[{"name":"inner_field","type":"string"}]}` is used for 'object' field: `{ "object" : { "inner_field" : "val" } }` * We can map all non-standard data types to record, like JavaScript (with scope) in the example below. The following schema: `{ "type":"record", "name":"javascriptwithscope", "fields":[ {"name":"$code","type":"string"}, {"name":"$scope","type":{"type":"record","name":"scope-object-record","fields"[{"name":"scope","type":"string"}]}} ] }` is used for 'javascriptwithscope' field: `{ "javascriptwithscope" : { "$code" : var l = 1; , "$scope" : { "scope" : "scope_val" } } }`
enum	-
map	Object The following schema: `{"type":"map","keys":"string","values":"string"}` is used for 'object' field: `{ "object" : { "inner_field" : "val" } }`
union	-

Approach

Move existing mongodb-plugins module to the mongodb-plugins project. Add MongoDB-specific properties to configuration, add support for MongoDB-specific datatypes. Update UI widgets JSON definitions.

MongoDB database plugin