Transformation rules and actions - AWS Database Migration Service
LimitationsValuesExamples

Transformation rules and actions

You use the transformation actions to specify any transformations you want to apply to the selected schema, table, or view. Transformation rules are optional.

Limitations

  • You can't apply more than one transformation rule action against the same object (schema, table, column, table-tablespace, or index-tablespace). You can apply several transformation rule actions on any level as long as each transformation action is applied against a different object. However, this restriction is not applicable when using data masking transformation rules where you can have another transformation like ADD-COLUMN or CHANGE-DATA-TYPE for the same column.

  • Table names and column names in transformation rules are case-sensitive. For example, you must provide table names and column names for an Oracle or Db2 database in upper-case.

  • Transformations are not supported for column names with Right-to-Left languages.

  • Transformations cannot be performed on columns that contain special characters (e.g. #, \, /, -) in their name.

  • The only supported transformation for columns that are mapped to BLOB/CLOB data types is to drop the column on the target.

  • AWS DMS doesn't support replicating two source tables to a single target table. AWS DMS replicates records from table to table, and from column to column, according to the replication task’s transformation rules. The object names must be unique to prevent overlapping.

    For example, a source table has a column named ID and the corresponding target table has a pre-existing column called id. If a rule uses an ADD-COLUMN statement to add a new column called id, and a SQLite statement to populate the column with custom values, this creates a duplicate, ambiguous object named id and is not supported.

  • When creating a transformation rule, we recommend using the data-type parameter only when the selection rules specify multiple columns, for instance, when you set column-name to %. We don't recommend using data-type for selecting a single column.

Values

For table-mapping rules that use the transformation rule type, you can apply the following values.

Parameter Possible values Description
rule-type transformation A value that applies the rule to each object specified by the selection rule. Use transformation unless otherwise noted.
rule-id A numeric value. A unique numeric value to identify the rule. If you specify multiple transformation rules for the same object (schema, table, column, inter-table space, or index table space), AWS DMS applies the transformation rule with the lower rule-id.
rule-name An alphanumeric value. A unique name to identify the rule.
object-locator An object with the following parameters:

  • schema-name – The name of the schema. For MongoDB and Amazon DocumentDB endpoints, this is the name of the database holding a set of collections.

  • table-name – The name of the table, view, or collection.

  • table-tablespace-name – The name of an existing table tablespace.

  • index-tablespace-name – The name of an existing index tablespace.

  • column-name – The name of an existing column.

  • data-type – The name of an existing column data type.

The name of each schema, table or view, table tablespace, index tablespace, and column to which the rule applies. You can use the "%" percent sign as a wildcard for all or part of the value of each object-locator parameter, except data-type. Thus, you can match these items:

  • A single table or view in a single schema

  • A single table or view in some or all schemas

  • Some or all tables and views in a single schema

  • Some or all tables and views in some or all schemas

  • One or more columns in the specified table or tables, view or views, and schema or schemas.

  • We recommend using the data-type parameter only when the selection rules specify multiple columns, for instance, when you set column-name to %. We don't recommend using this parameter for a single column.

Also, the table-tablespace-name or index-tablespace-name parameter is only available to match an Oracle source endpoint. You can specify either table-tablespace-name or index-tablespace-name in a single rule, but not both. Thus, you can match either of the following items:

  • One, some, or all table tablespaces

  • One, some, or all index tablespaces
rule-action

add-column, include-column, remove-column

rename

convert-lowercase, convert-uppercase

add-prefix, remove-prefix, replace-prefix

add-suffix, remove-suffix, replace-suffix

define-primary-key

change-data-type

add-before-image-columns

data-masking-digits-mask

data-masking-digits-randomize

data-masking-hash-mask

The transformation you want to apply to the object. All transformation rule actions are case-sensitive.

The add-column value of the rule-action parameter adds a column to a table. But you can't add a new column with the same name as an existing column of the same table.

When used with the expression and data-type parameters, add-column specifies the value of new column data.

The change-data-type value for rule-action is only available for column rule targets.

The include-column value of the rule-action parameter changes the mode of the table to drop all columns by default and include the columns specified. Multiple columns are included in the target by invoking the include-column rule multiple times.

You can't use a define-primary-key rule when the rule has a wildcard (%) in a schema or table name.

For an existing task, transformation rule actions which alter the target table schema such as remove-column, rename, or add-prefix will not take effect until you restart the task. If you resume the task after adding the transformation rule, you may see unexpected behavior for the altered column, which might include missing column data. A task restart is required to ensure the transformation rule works properly.

The data-masking-digits-mask, data-masking-digits-randomize, and data-masking-hash-mask are for masking sensitive information contained in one or more columns of the table when loading to target. These transformations are only available for column rule targets. For more details, see Using data masking to hide sensitive information

rule-target schema, table, column, table-tablespace, index-tablespace The type of object that you're transforming.

The table-tablespace and index-tablespace values are only available for an Oracle target endpoint.

Make sure to specify a value for the parameter that you specify as part of the object-locator: table-tablespace-name or index-tablespace-name name.
value An alphanumeric value that follows the naming rules for the target type. The new value for actions that require input, such as rename.
old-value An alphanumeric value that follows the naming rules for the target type. The old value for actions that require replacement, such as replace-prefix.
data-type

type – The data type to use if the rule-action is add-column or the replacement data type if therule-action is change-data-type.

Or, the name of the replacement data type when rule-action is change-data-type, the value of column-name is "%", and an additional data-type parameter to identify the existing data type is included in the object-locator.

AWS DMS supports column data type transformations for the following DMS data types: "bytes", "date", "time", "datetime", "int1", "int2", "int4", "int8", "numeric", "real4", "real8", "string", "uint1", "uint2", "uint4", "uint8", "wstring", "blob", "nclob", "clob", "boolean", "set", "list" "map", "tuple"

precision – If the added column or replacement data type has a precision, an integer value to specify the precision.

scale – If the added column or replacement data type has a scale, an integer value or date time value to specify the scale.

length – The length of new column data (when used with add-column)

The following is an example of a data-type parameter to specify the existing data type to be replaced. 

{
	"rules": [{
			"rule-type": "selection",
			"rule-id": "1",
			"rule-name": "1",
			"object-locator": {
				"schema-name": "%",
				"table-name": "%"
			},
			"rule-action": "include"
		},
		{
			"rule-type": "transformation",
			"rule-id": "2",
			"rule-name": "2",
			"rule-target": "column",
			"object-locator": {
				"schema-name": "test",
				"table-name": "table_t",
				"column-name": "col10"
			},
			"rule-action": "change-data-type",
			"data-type": {
				"type": "string",
				"length": "4092",
				"scale": ""
			}
		}
	]
}

Here, the col10 column of the table_t table is changed to the string data type.
expression An alphanumeric value that follows SQLite syntax.

When used with the rule-action set to rename-schema, the expression parameter specifies a new schema. When used with the rule-action set to rename-table, expression specifies a new table. When used with the rule-action set to rename-column, expression specifies a new column name value.

When used with the rule-action set to add-column, expression specifies data that makes up a new column.

Note that only expressions are supported for this parameter. Operators and commands are not supported.

For more information about using expressions for transformation rules, see Using transformation rule expressions to define column content.

For more information about SQLite expressions, see Using SQLite functions to build expressions.
primary-key-def

An object with the following parameters:

  • name – The name of a new primary key or unique index for the table or view.

  • (Optional) origin – The type of unique key to define: primary-key (the default) or unique-index.

  • columns – An array of strings listing the names of columns in the order they appear in the primary key or unique index.

 This parameter can define the name, type, and content of a unique key on the transformed table or view. It does so when the rule-action is set to define-primary-key and the rule-target is set to table. By default, the unique key is defined as a primary key.
before-image-def

An object with the following parameters:

  • column-prefix – A value prepended to a column name. The default value is BI_.

  • column-suffix – A value appended to the column name. The default is empty.

  • column-filter – Requires one of the following values: pk-only (default), non-lob (optional) and all (optional).

This parameter defines a naming convention to identify the before-image columns and specifies a filter to identify which source columns can have before-image columns created for them on the target. You can specify this parameter when the rule-action is set to add-before-image-columns and the rule-target is set to column.

Don't set both column-prefix and column-suffix to empty strings.

For column-filter, select:

  • pk-only – To add only columns that are part of table primary keys.

  • non-lob – To add only columns that are not of LOB type.

  • all – To add any column that has a before-image value.

For more information about before-image support for AWS DMS target endpoints, see:

Examples

Example Rename a schema

The following example renames a schema from Test in your source to Test1 in your target.

{

    "rules": [
        {
            "rule-type": "selection",
            "rule-id": "1",
            "rule-name": "1",
            "object-locator": {
                "schema-name": "Test",
                "table-name": "%"
            },
            "rule-action": "include"
        },
        {
            "rule-type": "transformation",
            "rule-id": "2",
            "rule-name": "2",
            "rule-action": "rename",
            "rule-target": "schema",
            "object-locator": {
                "schema-name": "Test"
            },
            "value": "Test1"
        }
    ]
}
Example Rename a table

The following example renames a table from Actor in your source to Actor1 in your target.

{
    "rules": [
        {
            "rule-type": "selection",
            "rule-id": "1",
            "rule-name": "1",
            "object-locator": {
                "schema-name": "Test",
                "table-name": "%"
            },
            "rule-action": "include"
        },
        {
            "rule-type": "transformation",
            "rule-id": "2",
            "rule-name": "2",
            "rule-action": "rename",
            "rule-target": "table",
            "object-locator": {
                "schema-name": "Test",
                "table-name": "Actor"
            },
            "value": "Actor1"
        }
    ]
}
Example Rename a column

The following example renames a column in table Actor from first_name in your source to fname in your target.

{
    "rules": [
        {
            "rule-type": "selection",
            "rule-id": "1",
            "rule-name": "1",
            "object-locator": {
                "schema-name": "test",
                "table-name": "%"
            },
            "rule-action": "include"
        },
         {
            "rule-type": "transformation",
            "rule-id": "4",
            "rule-name": "4",
            "rule-action": "rename",
            "rule-target": "column",
            "object-locator": {
                "schema-name": "test",
                "table-name": "Actor",
                "column-name" : "first_name"
            },
            "value": "fname"
        }
    ]
}
Example Rename an Oracle table tablespace

The following example renames the table tablespace named SetSpace for a table named Actor in your Oracle source to SceneTblSpace in your Oracle target endpoint.

{
    "rules": [
        {
            "rule-type": "selection",
            "rule-id": "1",
            "rule-name": "1",
            "object-locator": {
                "schema-name": "Play",
                "table-name": "%"
            },
            "rule-action": "include"
        },
        {
            "rule-type": "transformation",
            "rule-id": "2",
            "rule-name": "2",
            "rule-action": "rename",
            "rule-target": "table-tablespace",
            "object-locator": {
                "schema-name": "Play",
                "table-name": "Actor",
                "table-tablespace-name": "SetSpace"
            },
            "value": "SceneTblSpace"
        }
    ]
}
Example Rename an Oracle index tablespace

The following example renames the index tablespace named SetISpace for a table named Actor in your Oracle source to SceneIdxSpace in your Oracle target endpoint.

{
    "rules": [
        {
            "rule-type": "selection",
            "rule-id": "1",
            "rule-name": "1",
            "object-locator": {
                "schema-name": "Play",
                "table-name": "%"
            },
            "rule-action": "include"
        },
        {
            "rule-type": "transformation",
            "rule-id": "2",
            "rule-name": "2",
            "rule-action": "rename",
            "rule-target": "table-tablespace",
            "object-locator": {
                "schema-name": "Play",
                "table-name": "Actor",
                "table-tablespace-name": "SetISpace"
            },
            "value": "SceneIdxSpace"
        }
    ]
}
Example Add a column

The following example adds a datetime column to the table Actor in schema test.

{
    "rules": [
        {
            "rule-type": "selection",
            "rule-id": "1",
            "rule-name": "1",
            "object-locator": {
                "schema-name": "test",
                "table-name": "%"
            },
            "rule-action": "include"
        },
        {
            "rule-type": "transformation",
            "rule-id": "2",
            "rule-name": "2",
            "rule-action": "add-column",
            "rule-target": "column",
            "object-locator": {
                "schema-name": "test",
                "table-name": "actor"
            },
            "value": "last_updated",
            "data-type": {
                "type": "datetime",
                "precision": 6
            }
        }
    ]
}
Example Remove a column

The following example transforms the table named Actor in your source to remove all columns starting with the characters col from it in your target.

{
 	"rules": [{
		"rule-type": "selection",
		"rule-id": "1",
		"rule-name": "1",
		"object-locator": {
			"schema-name": "test",
			"table-name": "%"
		},
		"rule-action": "include"
	}, {
		"rule-type": "transformation",
		"rule-id": "2",
		"rule-name": "2",
		"rule-action": "remove-column",
		"rule-target": "column",
		"object-locator": {
			"schema-name": "test",
			"table-name": "Actor",
			"column-name": "col%"
		}
	}]
 }
Example Convert to lowercase

The following example converts a table name from ACTOR in your source to actor in your target.

{
	"rules": [{
		"rule-type": "selection",
		"rule-id": "1",
		"rule-name": "1",
		"object-locator": {
			"schema-name": "test",
			"table-name": "%"
		},
		"rule-action": "include"
	}, {
		"rule-type": "transformation",
		"rule-id": "2",
		"rule-name": "2",
		"rule-action": "convert-lowercase",
		"rule-target": "table",
		"object-locator": {
			"schema-name": "test",
			"table-name": "ACTOR"
		}
	}]
}
Example Convert to uppercase

The following example converts all columns in all tables and all schemas from lowercase in your source to uppercase in your target.

{
    "rules": [
        {
            "rule-type": "selection",
            "rule-id": "1",
            "rule-name": "1",
            "object-locator": {
                "schema-name": "test",
                "table-name": "%"
            },
            "rule-action": "include"
        },
        {
            "rule-type": "transformation",
            "rule-id": "2",
            "rule-name": "2",
            "rule-action": "convert-uppercase",
            "rule-target": "column",
            "object-locator": {
                "schema-name": "%",
                "table-name": "%",
                "column-name": "%"
            }
        }
    ]
}
Example Add a prefix

The following example transforms all tables in your source to add the prefix DMS_ to them in your target.

{
 	"rules": [{
		"rule-type": "selection",
		"rule-id": "1",
		"rule-name": "1",
		"object-locator": {
			"schema-name": "test",
			"table-name": "%"
		},
		"rule-action": "include"
	}, {
		"rule-type": "transformation",
		"rule-id": "2",
		"rule-name": "2",
		"rule-action": "add-prefix",
		"rule-target": "table",
		"object-locator": {
			"schema-name": "test",
			"table-name": "%"
		},
		"value": "DMS_"
	}]
 
}
Example Replace a prefix

The following example transforms all columns containing the prefix Pre_ in your source to replace the prefix with NewPre_ in your target.

{
    "rules": [
        {
            "rule-type": "selection",
            "rule-id": "1",
            "rule-name": "1",
            "object-locator": {
                "schema-name": "test",
                "table-name": "%"
            },
            "rule-action": "include"
        },
        {
            "rule-type": "transformation",
            "rule-id": "2",
            "rule-name": "2",
            "rule-action": "replace-prefix",
            "rule-target": "column",
            "object-locator": {
                "schema-name": "%",
                "table-name": "%",
                "column-name": "%"
            },
            "value": "NewPre_",
            "old-value": "Pre_"
        }
    ]
}
Example Remove a suffix

The following example transforms all tables in your source to remove the suffix _DMS from them in your target.

{
	"rules": [{
		"rule-type": "selection",
		"rule-id": "1",
		"rule-name": "1",
		"object-locator": {
			"schema-name": "test",
			"table-name": "%"
		},
		"rule-action": "include"
	}, {
		"rule-type": "transformation",
		"rule-id": "2",
		"rule-name": "2",
		"rule-action": "remove-suffix",
		"rule-target": "table",
		"object-locator": {
			"schema-name": "test",
			"table-name": "%"
		},
		"value": "_DMS"
	}]
}
Example Define a primary key

The following example defines a primary key named ITEM-primary-key on three columns of the ITEM table migrated to your target endpoint.

{
	"rules": [{
		"rule-type": "selection",
		"rule-id": "1",
		"rule-name": "1",
		"object-locator": {
			"schema-name": "inventory",
			"table-name": "%"
		},
		"rule-action": "include"
	}, {
		"rule-type": "transformation",
		"rule-id": "2",
		"rule-name": "2",
		"rule-action": "define-primary-key",
		"rule-target": "table",
		"object-locator": {
			"schema-name": "inventory",
			"table-name": "ITEM"
		},
		"primary-key-def": {
			"name": "ITEM-primary-key",
			"columns": [
				"ITEM-NAME",
				"BOM-MODEL-NUM",
				"BOM-PART-NUM"
			]
              }
	}]
}
Example Define a unique index

The following example defines a unique index named ITEM-unique-idx on three columns of the ITEM table migrated to your target endpoint.

{
	"rules": [{
		"rule-type": "selection",
		"rule-id": "1",
		"rule-name": "1",
		"object-locator": {
			"schema-name": "inventory",
			"table-name": "%"
		},
		"rule-action": "include"
	}, {
		"rule-type": "transformation",
		"rule-id": "2",
		"rule-name": "2",
		"rule-action": "define-primary-key",
		"rule-target": "table",
		"object-locator": {
			"schema-name": "inventory",
			"table-name": "ITEM"
		},
		"primary-key-def": {
			"name": "ITEM-unique-idx",
			"origin": "unique-index",
			"columns": [
				"ITEM-NAME",
				"BOM-MODEL-NUM",
				"BOM-PART-NUM"
			]
              }
	}]
}
Example Change data type of target column

The following example changes the data type of a target column named SALE_AMOUNT from an existing data type to int8.

{
    "rule-type": "transformation",
    "rule-id": "1",
    "rule-name": "RuleName 1",
    "rule-action": "change-data-type",
    "rule-target": "column",
    "object-locator": {
        "schema-name": "dbo",
        "table-name": "dms",
        "column-name": "SALE_AMOUNT"
    },
    "data-type": {
        "type": "int8"
    }
}
Example Add a before image column

For a source column named emp_no, the transformation rule in the example following adds a new column named BI_emp_no in the target.

{
	"rules": [{
			"rule-type": "selection",
			"rule-id": "1",
			"rule-name": "1",
			"object-locator": {
				"schema-name": "%",
				"table-name": "%"
			},
			"rule-action": "include"
		},
		{
			"rule-type": "transformation",
			"rule-id": "2",
			"rule-name": "2",
			"rule-target": "column",
			"object-locator": {
				"schema-name": "%",
				"table-name": "employees"
			},
			"rule-action": "add-before-image-columns",
			"before-image-def": {
				"column-prefix": "BI_",
				"column-suffix": "",
				"column-filter": "pk-only"
			}
		}
	]
}

Here, the following statement populates a BI_emp_no column in the corresponding row with 1.

UPDATE employees SET emp_no = 3 WHERE BI_emp_no = 1;

When writing CDC updates to supported AWS DMS targets, the BI_emp_no column makes it possible to tell which rows have updated values in the emp_no column.