Datasets in Azure Data Factory and Azure Synapse Analytics

APPLIES TO: Azure Data Factory Azure Synapse Analytics

This article describes what datasets are, how they're defined in JSON format, and how they're used in Azure Data Factory and Synapse pipelines.

If you're new to Data Factory, see Introduction to Azure Data Factory for an overview. For more information about Azure Synapse, see What is Azure Synapse

Overview

An Azure Data Factory or Synapse workspace can have one or more pipelines. A pipeline is a logical grouping of activities that together perform a task. The activities in a pipeline define actions to perform on your data. Now, a dataset is a named view of data that simply points or references the data you want to use in your activities as inputs and outputs. Datasets identify data within different data stores, such as tables, files, folders, and documents. For example, an Azure Blob dataset specifies the blob container and folder in Blob Storage from which the activity should read the data.

Before you create a dataset, you must create a linked service to link your data store to the service. Linked services are much like connection strings, which define the connection information needed for the service to connect to external resources. Think of it this way; the dataset represents the structure of the data within the linked data stores, and the linked service defines the connection to the data source. For example, an Azure Storage linked service links a storage account. An Azure Blob dataset represents the blob container and the folder within that Azure Storage account that contains the input blobs to be processed.

Here's a sample scenario. To copy data from Blob storage to a SQL Database, you create two linked services: Azure Blob Storage and Azure SQL Database. Then, create two datasets: Delimited Text dataset (which refers to the Azure Blob Storage linked service, assuming you have text files as source) and Azure SQL Table dataset (which refers to the Azure SQL Database linked service). The Azure Blob Storage and Azure SQL Database linked services contain connection strings that the service uses at runtime to connect to your Azure Storage and Azure SQL Database, respectively. The Delimited Text dataset specifies the blob container and blob folder that contains the input blobs in your Blob storage, along with format-related settings. The Azure SQL Table dataset specifies the SQL table in your SQL Database to which the data is to be copied.

The following diagram shows the relationships among pipeline, activity, dataset, and linked services:

Create a dataset with UI

Dataset JSON

A dataset is defined in the following JSON format:

{
    "name": "<name of dataset>",
    "properties": {
        "type": "<type of dataset: DelimitedText, AzureSqlTable etc...>",
        "linkedServiceName": {
                "referenceName": "<name of linked service>",
                "type": "LinkedServiceReference",
        },
        "schema":[

        ],
        "typeProperties": {
            "<type specific property>": "<value>",
            "<type specific property 2>": "<value 2>",
        }
    }
}

The following table describes properties in the above JSON:

When you import the schema of dataset, select the Import Schema button and choose to import from the source or from a local file. In most cases, you'll import the schema directly from the source. But if you already have a local schema file (a Parquet file or CSV with headers), you can direct the service to base the schema on that file.

In copy activity, datasets are used in source and sink. Schema defined in dataset is optional as reference. If you want to apply column/field mapping between source and sink, refer to Schema and type mapping.

In Data Flow, datasets are used in source and sink transformations. The datasets define the basic data schemas. If your data has no schema, you can use schema drift for your source and sink. Metadata from the datasets appears in your source transformation as the source projection. The projection in the source transformation represents the Data Flow data with defined names and types.

Dataset type

The service supports many different types of datasets, depending on the data stores you use. You can find the list of supported data stores from Connector overview article. Select a data store to learn how to create a linked service and a dataset for it.

For example, for a Delimited Text dataset, the dataset type is set to DelimitedText as shown in the following JSON sample:

{
    "name": "DelimitedTextInput",
    "properties": {
        "linkedServiceName": {
            "referenceName": "AzureBlobStorage",
            "type": "LinkedServiceReference"
        },
        "annotations": [],
        "type": "DelimitedText",
        "typeProperties": {
            "location": {
                "type": "AzureBlobStorageLocation",
                "fileName": "input.log",
                "folderPath": "inputdata",
                "container": "adfgetstarted"
            },
            "columnDelimiter": ",",
            "escapeChar": "\\",
            "quoteChar": "\""
        },
        "schema": []
    }
}

Create datasets

You can create datasets by using one of these tools or SDKs: .NET API, PowerShell, REST API, Azure Resource Manager Template, and Azure portal

Related content

See the following tutorial for step-by-step instructions for creating pipelines and datasets by using one of these tools or SDKs.

• Quickstart: create a data factory using .NET
• Quickstart: create a data factory using PowerShell
• Quickstart: create a data factory using REST API
• Quickstart: create a data factory using Azure portal