Lookup activity in Azure Data Factory and Azure Synapse Analytics

APPLIES TO: 👁 Image
Azure Data Factory 👁 Image
Azure Synapse Analytics

Lookup activity can retrieve a dataset from any of the data sources supported by data factory and Synapse pipelines. You can use it to dynamically determine which objects to operate on in a subsequent activity, instead of hard coding the object name. Some object examples are files and tables.

Lookup activity reads and returns the content of a configuration file or table. It also returns the result of executing a query or stored procedure. The output can be a singleton value or an array of attributes, which can be consumed in a subsequent copy, transformation, or control flow activities like ForEach activity.

Create a Lookup activity with UI

To use a Lookup activity in a pipeline, complete the following steps:

1. Search for Lookup in the pipeline Activities pane, and drag a Lookup activity to the pipeline canvas.

2. Select the new Lookup activity on the canvas if it is not already selected, and its Settings tab, to edit its details.

   👁 Shows the UI for a Lookup activity.
   

3. Choose an existing source dataset or select the New button to create a new one.

4. The options for identifying rows to include from the source dataset will vary based on the dataset type. The example above shows the configuration options for a delimited text dataset. Below are examples of configuration options for an Azure SQL table dataset and an OData dataset.

   👁 Shows the configuration options in the Lookup activity for an Azure SQL table dataset.
   

   👁 Shows the configuration options in the Lookup activity for an OData dataset.
   

Supported capabilities

Note the following:

• The Lookup activity can return up to 5000 rows; if the result set contains more records, the first 5000 rows will be returned.
• The Lookup activity output supports up to 4 MB in size, activity will fail if the size exceeds the limit.
• The longest duration for Lookup activity before time-out is 24 hours.

The following data sources are supported for Lookup activity.

Syntax

{
 "name":"LookupActivity",
 "type":"Lookup",
 "typeProperties":{
 "source":{
 "type":"<source type>"
 },
 "dataset":{
 "referenceName":"<source dataset name>",
 "type":"DatasetReference"
 },
 "firstRowOnly":<true or false>
 }
}

Type properties

Use the Lookup activity result

The lookup result is returned in the output section of the activity run result.

• When firstRowOnly is set to true (default), the output format is as shown in the following code. The lookup result is under a fixed firstRow key. To use the result in subsequent activity, use the pattern of @{activity('LookupActivity').output.firstRow.table}.

  {
   "firstRow":
   {
   "Id": "1",
   "schema":"dbo",
   "table":"Table1"
   }
  }
  

• When firstRowOnly is set to false, the output format is as shown in the following code. A count field indicates how many records are returned. Detailed values are displayed under a fixed value array. In such a case, the Lookup activity is followed by a Foreach activity. You pass the value array to the ForEach activity items field by using the pattern of @activity('MyLookupActivity').output.value. To access elements in the value array, use the following syntax: @{activity('lookupActivity').output.value[zero based index].propertyname}. An example is @{activity('lookupActivity').output.value[0].schema}.

  {
   "count": "2",
   "value": [
   {
   "Id": "1",
   "schema":"dbo",
   "table":"Table1"
   },
   {
   "Id": "2",
   "schema":"dbo",
   "table":"Table2"
   }
   ]
  } 
  

Example

In this example, the pipeline contains two activities: Lookup and Copy. The Copy Activity copies data from a SQL table in your Azure SQL Database instance to Azure Blob storage. The name of the SQL table is stored in a JSON file in Blob storage. The Lookup activity looks up the table name at runtime. JSON is modified dynamically by using this approach. You don't need to redeploy pipelines or datasets.

This example demonstrates lookup for the first row only. For lookup for all rows and to chain the results with ForEach activity, see the samples in Copy multiple tables in bulk.

Pipeline

• The Lookup activity is configured to use LookupDataset, which refers to a location in Azure Blob storage. The Lookup activity reads the name of the SQL table from a JSON file in this location.
• The Copy Activity uses the output of the Lookup activity, which is the name of the SQL table. The tableName property in the SourceDataset is configured to use the output from the Lookup activity. Copy Activity copies data from the SQL table to a location in Azure Blob storage. The location is specified by the SinkDataset property.

{
 "name": "LookupPipelineDemo",
 "properties": {
 "activities": [
 {
 "name": "LookupActivity",
 "type": "Lookup",
 "dependsOn": [],
 "policy": {
 "timeout": "7.00:00:00",
 "retry": 0,
 "retryIntervalInSeconds": 30,
 "secureOutput": false,
 "secureInput": false
 },
 "userProperties": [],
 "typeProperties": {
 "source": {
 "type": "JsonSource",
 "storeSettings": {
 "type": "AzureBlobStorageReadSettings",
 "recursive": true
 },
 "formatSettings": {
 "type": "JsonReadSettings"
 }
 },
 "dataset": {
 "referenceName": "LookupDataset",
 "type": "DatasetReference"
 },
 "firstRowOnly": true
 }
 },
 {
 "name": "CopyActivity",
 "type": "Copy",
 "dependsOn": [
 {
 "activity": "LookupActivity",
 "dependencyConditions": [
 "Succeeded"
 ]
 }
 ],
 "policy": {
 "timeout": "7.00:00:00",
 "retry": 0,
 "retryIntervalInSeconds": 30,
 "secureOutput": false,
 "secureInput": false
 },
 "userProperties": [],
 "typeProperties": {
 "source": {
 "type": "AzureSqlSource",
 "sqlReaderQuery": {
 "value": "select * from [@{activity('LookupActivity').output.firstRow.schema}].[@{activity('LookupActivity').output.firstRow.table}]",
 "type": "Expression"
 },
 "queryTimeout": "02:00:00",
 "partitionOption": "None"
 },
 "sink": {
 "type": "DelimitedTextSink",
 "storeSettings": {
 "type": "AzureBlobStorageWriteSettings"
 },
 "formatSettings": {
 "type": "DelimitedTextWriteSettings",
 "quoteAllText": true,
 "fileExtension": ".txt"
 }
 },
 "enableStaging": false,
 "translator": {
 "type": "TabularTranslator",
 "typeConversion": true,
 "typeConversionSettings": {
 "allowDataTruncation": true,
 "treatBooleanAsNumber": false
 }
 }
 },
 "inputs": [
 {
 "referenceName": "SourceDataset",
 "type": "DatasetReference",
 "parameters": {
 "schemaName": {
 "value": "@activity('LookupActivity').output.firstRow.schema",
 "type": "Expression"
 },
 "tableName": {
 "value": "@activity('LookupActivity').output.firstRow.table",
 "type": "Expression"
 }
 }
 }
 ],
 "outputs": [
 {
 "referenceName": "SinkDataset",
 "type": "DatasetReference",
 "parameters": {
 "schema": {
 "value": "@activity('LookupActivity').output.firstRow.schema",
 "type": "Expression"
 },
 "table": {
 "value": "@activity('LookupActivity').output.firstRow.table",
 "type": "Expression"
 }
 }
 }
 ]
 }
 ],
 "annotations": [],
 "lastPublishTime": "2020-08-17T10:48:25Z"
 }
}

Lookup dataset

The lookup dataset is the sourcetable.json file in the Azure Storage lookup folder specified by the AzureBlobStorageLinkedService type.

{
 "name": "LookupDataset",
 "properties": {
 "linkedServiceName": {
 "referenceName": "AzureBlobStorageLinkedService",
 "type": "LinkedServiceReference"
 },
 "annotations": [],
 "type": "Json",
 "typeProperties": {
 "location": {
 "type": "AzureBlobStorageLocation",
 "fileName": "sourcetable.json",
 "container": "lookup"
 }
 }
 }
}

Source dataset for Copy Activity

The source dataset uses the output of the Lookup activity, which is the name of the SQL table. Copy Activity copies data from this SQL table to a location in Azure Blob storage. The location is specified by the sink dataset.

{
 "name": "SourceDataset",
 "properties": {
 "linkedServiceName": {
 "referenceName": "AzureSqlDatabase",
 "type": "LinkedServiceReference"
 },
 "parameters": {
 "schemaName": {
 "type": "string"
 },
 "tableName": {
 "type": "string"
 }
 },
 "annotations": [],
 "type": "AzureSqlTable",
 "schema": [],
 "typeProperties": {
 "schema": {
 "value": "@dataset().schemaName",
 "type": "Expression"
 },
 "table": {
 "value": "@dataset().tableName",
 "type": "Expression"
 }
 }
 }
}

Sink dataset for Copy Activity

Copy Activity copies data from the SQL table to the filebylookup.csv file in the csv folder in Azure Storage. The file is specified by the AzureBlobStorageLinkedService property.

{
 "name": "SinkDataset",
 "properties": {
 "linkedServiceName": {
 "referenceName": "AzureBlobStorageLinkedService",
 "type": "LinkedServiceReference"
 },
 "parameters": {
 "schema": {
 "type": "string"
 },
 "table": {
 "type": "string"
 }
 },
 "annotations": [],
 "type": "DelimitedText",
 "typeProperties": {
 "location": {
 "type": "AzureBlobStorageLocation",
 "fileName": {
 "value": "@{dataset().schema}_@{dataset().table}.csv",
 "type": "Expression"
 },
 "container": "csv"
 },
 "columnDelimiter": ",",
 "escapeChar": "\\",
 "quoteChar": "\""
 },
 "schema": []
 }
}

sourcetable.json

You can use following two kinds of formats for sourcetable.json file.

Set of objects

{
 "Id":"1",
 "schema":"dbo",
 "table":"Table1"
}
{
 "Id":"2",
 "schema":"dbo",
 "table":"Table2"
}

Array of objects

[ 
 {
 "Id": "1",
 "schema":"dbo",
 "table":"Table1"
 },
 {
 "Id": "2",
 "schema":"dbo",
 "table":"Table2"
 }
]

Limitations and workarounds

Here are some limitations of the Lookup activity and suggested workarounds.

Related content

See other control flow activities supported by Azure Data Factory and Synapse pipelines:

• Execute Pipeline activity
• ForEach activity
• GetMetadata activity
• Web activity