How to transfer the data from one db to another using azure datafactory ( ADF ) ?

 Steps:

1) Create Azure Datafactory 

2)  Create Linked service 

3) Add the dataset to the linked service.

az cosmosdb list-connection-strings --name <> --resource-group ..

az datafactory linked-service create --resource-group <> --factory-name <> --properties "@MongoDBAPILinkedService.json" --name TigerLinkedSource

@MongoDBAPILinkedService.json

{
    "type": "CosmosDbMongoDbApi",
    "typeProperties": {
        "connectionString": "mongodb://**********:primarypassword@*****************.documents.azure.com:10255/?ssl=true&replicaSet=globaldb",
        "database": "tiger-db"
    }
}
step3:
adding the dataset
// source dataset az datafactory dataset create --resource-group <> --factory-name  <> --dataset-name OutputDataset --properties "@MongoDBAPIDatasetSource.json"{
    "linkedServiceName": {
      "referenceName": "TigerLinkedSource",
      "type": "LinkedServiceReference"
    },
    "annotations": [],
    "type": "CosmosDbMongoDbApiCollection",
    "schema": [],
    "typeProperties": {
      "collection": "tiger"
    }
  }
Please do the above process for the sink.
Create a pipeline in between the source and sink & trigger/run the pipeline using azure cli.
az datafactory pipeline create --resource-group <> --factory-name <> --name Pipeline --pipeline "@Pipeline.json"
Pipeline.json
{
    "activities": [
        {
            "name": "CopyFromSourceToSink",
            "type": "Copy",
            "dependsOn": [],
            "policy": {
                "timeout": "7.00:00:00",
                "retry": 0,
                "retryIntervalInSeconds": 30,
                "secureOutput": false,
                "secureInput": false
            },
            "userProperties": [],
            "typeProperties": {
                "source": {
                    "type": "CosmosDbMongoDbApiSource",
                     "batchSize":100
                 },
                "sink": {
                    "type": "CosmosDbMongoDbApiSink",
                    "writeBatchTimeout": "00:30:00",
                    "writeBehavior": "insert"
                },
                "enableStaging": false
            },
            "inputs": [
                {
                    "referenceName": "InputDataset",
                    "type": "DatasetReference"
                }
            ],
            "outputs": [
                {
                    "referenceName": "OutputDataset",
                    "type": "DatasetReference"
                }
            ]
        }
    ]
}
trigger/run the pipeline using this azure cli command.
az datafactory pipeline create-run --resource-group <> --factory-name <> --name Pipeline