Help Center/ EventGrid/ User Guide/ Event Rules/ Event Content Transformation
Updated on 2025-07-07 GMT+08:00
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Event Content Transformation

EG transforms CloudEvents-compliant events so that they can be processed by specified targets.

Supported transform types: pass-through, variables, constants.

Constraints

When using the variable transformation type, the event stream cannot transform fields in the source message content.

Pass-through

Directly route CloudEvents-compliant events to the target. Example:

Before Transformation

Transform Type

After Transformation

 
{
    "events":[{
	"id": "4b26115b-73e-cf74a******",
        "specversion": "1.0",
	"source": "HC.OBS",
	"type": "object:put",
	"datacontenttype": "application/json",
	"subject": "xxx.jpg",
	"time": "2022-01-17T12:07:48.955Z",
	"data": {
		"name": "test01",
		"state": "enable"
	}
    }]
}

Pass-through

 
{
    "events":[{
	"id": "4b26115b-73e-cf74******",
        "specversion": "1.0",
	"source": "HC.OBS",
	"type": "object:put",
	"datacontenttype": "application/json",
	"subject": "xxx.jpg",
	"time": "2022-01-17T12:07:48.955Z",
	"data": {
		"name": "test01",
		"state": "enable"
	}
    }]
}

Variables

Route variables in CloudEvents-compliant events to the target by using a template. Example:

Before Transformation

Transform Type

After Transformation

 
{
    "events":[{
	"id": "4b26115b-73e-cf74a******",
        "specversion": "1.0",
	"source": "HC.OBS",
	"type": "object:put",
	"datacontenttype": "application/json",
	"subject": "xxx.jpg",
	"time": "2022-01-17T12:07:48.955Z",
	"data": {
		"name": "test01",
		"state": "enable"
	}
    }]
}

Parameter

{"name":"$.data.name"}

Template

My name is ${name}

If the event target is FunctionGraph (function computing), the template must be in JSON format. Example:

{"name":"${name}"}
 
My name is test01
NOTE:

If the event target is FunctionGraph (function computing), the transformation result is as follows:

{"name": "test01"}

Example of complex transformation from OBS to EG and then to FunctionGraph:

Before Transformation

Transform Type

After Transformation

 
{
    "specversion": "1.0",
    "id": "******9db447aa3******",
    "source": "HC.OBS.DWR",
    "type": "OBS:DWR:ObjectCreated:PUT",
    "datacontenttype": "application/json",
    "dataschema": "",
    "subject": "test.txt",
    "time": "2023-08-01T11:41:51.712759419Z",
    "ttl": "4000",
    "data": {
        "eventVersion": "3.0",
        "eventSource": "OBS",
        "eventRegion": "cn-north-4",
        "eventTime": "2023-08-01T19:41:47.879Z",
        "eventName": "ObjectCreated:Put",
        "userIdentity": {
            "ID": "******fef0f08c******"
        },
        "requestParameters": {
            "sourceIPAddress": "1**.1**.1**.1**"
        },
        "responseElements": {
            "x-obs-request-id": "******47aa3cdafb******",
            "x-obs-id-2": "",
            "x-amz-request-id": "",
            "x-amz-id-2": ""
        },
        "obs": {
            "Version": "1.0",
            "configurationId": "******4aaac1******",
            "bucket": {
                "name": "test",
                "ownerIdentity": {
                    "ID": "******f1234567******"
                },
                "bucket": "test",
                "arn": ""
            },
            "object": {
                "key": "test.txt",
                "eTag": "******48ce552c3******",
                "size": 13,
                "versionId": "******BE7FFFF******",
                "sequencer": "1",
                "oldpsxpth": ""
            }
        }
    }
}

Parameters

{
  "eventVersion": "$.data.eventVersion",
  "eventTime": "$.data.eventTime",
  "requestParameters": "$.data.requestParameters.sourceIPAddress",
  "configurationId": "$.data.obs.configurationId",
  "eTag": "$.data.obs.object.eTag",
  "sequencer": "$.data.obs.object.sequencer",
  "key": "$.data.obs.object.key",
  "size": "$.data.obs.object.size",
  "arn": "$.data.obs.bucket.arn",
  "name": "$.data.obs.bucket.name",
  "ownerIdentity": "$.data.obs.bucket.ownerIdentity.ID",
  "Region": "$.data.eventRegion",
  "eventName": "$.type",
  "userIdentity": "$.data.userIdentity.ID"
}

Template

{
    "Records": [
        {
            "eventVersion": "${eventVersion}",
            "eventTime": "${eventTime}",
            "requestParameters": {
                "sourceIPAddress": "${requestParameters}"
            },
            "obs": {
                "configurationId": "${configurationId}",
                "object": {
                    "eTag": "${eTag}",
                    "sequencer": "${sequencer}",
                    "key": "${key}",
                    "size": "${size}"
                },
                "bucket": {
                    "arn": "${arn}",
                    "name": "${name}",
                    "ownerIdentity": {
                        "PrincipalId": "${ownerIdentity}"
                    }
                }
            },
            "Region": "${Region}",
            "eventName": "${eventName}",
            "userIdentity": {
                "principalId": "${userIdentity}"
            }
        }
    ]
}

The value in the template is the key of the corresponding parameter.

 
{
    "Records": [
        {
            "eventVersion": "3.0",
            "eventTime": "2023-08-01T19:41:47.879Z",
            "requestParameters": {
                "sourceIPAddress": "1**.1**.1**.1**"
            },
            "obs": {
                "configurationId": "******4aaac1******",
                "object": {
                    "eTag": "******48ce552c3******",
                    "sequencer": "1",
                    "key": "test.txt",
                    "size": "13"
                },
                "bucket": {
                    "arn": "",
                    "name": "test",
                    "ownerIdentity": {
                        "PrincipalId": "******f1234567******"
                    }
                }
            },
            "Region": "cn-north-4",
            "eventName": "OBS:DWR:ObjectCreated:PUT",
            "userIdentity": {
                "principalId": "******fef0f08c******"
            }
        }
    ]
}

Constants

Route constants in events to the target. Example:

Before Transformation

Rule

After Transformation

 
{
    "events":[{
	"id": "4b26115b-73cf74a******",
        "specversion": "1.0",
	"source": "HC.OBS",
	"type": "object:put",
	"datacontenttype": "application/json",
	"subject": "xxx.jpg",
	"time": "2022-01-17T12:07:48.955Z",
	"data": {
		"name": "test01",
		"state": "enable"
	}
    }]
}

Parameter

test01

If the event target is FunctionGraph (function computing), the rule must be in JSON format. Example:

{"name": "test01"}
 
test01
NOTE:

If the event target is FunctionGraph (function computing), the transformation result is as follows:

{"name": "test01"}

More Examples

  1. After you set a DMS for RabbitMQ or DMS for RocketMQ event source for a subscription, messages will contain the context field in data after being transformed to CloudEvents-compliant events. If you set the transform type to Variables for the event target, the rule must also contain the context field. Example:

    Before Transformation

    Transform Type

    After Transformation

    		 
    {
    "type": "ROCKETMQ:CloudTrace:RocketmqCall",
    "data": {
        "context": {    
		"name": "test01",
		"state": "enable"
         }
    },
    "source": "zhang_roc",
    "time": "2023-02-01T10:47:07Z",
    "datacontenttype": "application/json",
    "specversion": "1.0",
    "id": "2f885496-570c-4925-82fd-d1ad09******",
    "subject": "ROCKETMQ:cn-north-7:eec88b34-9470-483e-8961-edb168******/0de095e33e00d36e2fd2c0019a******:ROCKETMQ:zhang_roc"
}

    Parameter

    {"name":"$.data.context.name"}

    Template

    My name is ${name}
    		 
    My name is test01
  2. If you set Event Target to FunctionGraph (function computing) and Transform Type to Pass-through in 8, the event content cannot be transferred to the event target as the input value. To do it, you can use Variables or Constants transform type and configure input field in the rule. The following is an example:
    Table 1 Variables type example

    Before Transformation

    Rule

    After Transformation

    		 
    {
    "events":[{
	"id": "4b26115b-73cf74a******",
        "specversion": "1.0",
	"source": "HC.OBS",
	"type": "object:put",
	"datacontenttype": "application/json",
	"subject": "xxx.jpg",
	"time": "2022-01-17T12:07:48.955Z",
	"data": {
		"name": "test01",
		"state": "enable"
	}
    }]
}

    Variable

    {"data": "$.data"}

    Template

    {"input": ${data}}

    		 
    {
	"input": {
		"name": "test01",
		"state": "enable"
	}
}
    Table 2 Constants type example

    Before Transformation

    Rule

    After Transformation

    		 
    {
    "events":[{
	"id": "4b26115b-73cf74a******",
        "specversion": "1.0",
	"source": "HC.OBS",
	"type": "object:put",
	"datacontenttype": "application/json",
	"subject": "xxx.jpg",
	"time": "2022-01-17T12:07:48.955Z",
	"data": {
		"name": "test01",
		"state": "enable"
	}
    }]
}

    Constant

    {
	"input": {
		"name": "test01"
	}
}
    		 
    {
	"input": {
		"name": "test01"
	}
}
Parent topic: Event Rules