tMap expression syntax

Shicong Hong
Talend Data Fabric
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Talend Studio

tMap expression syntax

This article introduces the syntax to use in the Expression Builder, to help you understand and use the tMap component. The tMap is one of the core components of Talend Studio and is used very often in Jobs. The tMap component is primarily used for mapping input fields to output fields and transforming the input data in the Expression Builder of the corresponding output column.

This procedure was written with:

  • Talend Open Studio for Data Integration 5.2.0
  • Sun JDK build 1.6.0_26-b03
  • Windows XP SP3

This procedure applies to all versions of Talend Studio.

DescriptionMapping Expressions

The Expression Builder allows you to type in a mapping expression for each column in each output table. This article presents the following syntax examples:

  • Basic mapping
  • Arithmetic operation
  • Calling Java class method
  • Calling Talend Routine
  • If / else statement
Basic mapping

The tMap provides a graphical tool called Map Editor that allows you to create the mapping more easily from the input table to the output table using a simple drag-and-drop action. The following screenshot shows a simple mapping without any transformation from the input table to the output table. (Click the picture to see a full size image)

In the above screenshot, you can see the format used to map the input column in the Expression Builder of the corresponding output column is: rowName.columnName, row1.customer_id in this example. row1 is the row identifier of the input table, it is not a constant, it may change according to your Job. You can always read it at the top of each input table.

Concatenating fields

You can concatenate multiple fields using the + character in the Expression Builder. As long as the type of at least one of the fields is string, the multiple strings are connected, as shown below.

Setting output column with a constant

You can set a constant to an output column in the Expression Builder, without mapping from the input columns. As shown below, the company column of string type is set to a fixed value, Talend .

The input data will be transformed to output data after being processed into the tMap .

Input table

employee_id name
1 Elisa
2 Nicolas
3 Patrick

Output table

employee_id name company
1 Elisa Talend
2 Nicolas Talend
3 Patrick Talend

The data type of the value in the Expression Builder should be consistent with the data type of the output column. Otherwise, it will throw a Java compilation error. For example, if a constant 1 is set to company column in the Expression Builder, it will throw a compilation error when the Job is executed: "Type mismatch: cannot convert from int to String" , because the data type of the company column is defined as string, but an Integer/int value is set for this column.

Arithmetic operation

You can perform arithmetic operations i ncluding additions, subtractions, multiplications and divisions in the Expression Builder.

As shown below, there is a new column called new_salary in the output table. Its value is the original salary plus 500.

The input data will be transformed to output data after being processed in the tMap .

Input table

employee_id name salary
1 Elisa 12000
2 Nicolas 13000
3 Patrick 10000

Output table

employee_id name salary new_salary
1 Elisa 12000 12500
2 Nicolas 13000 13500
3 Patrick 10000 10500
Calling a Java class method

You can call a Java class method to transform the input fields in the Expression Builder. Call the Java method to achieve the following task: cut the first 4 characters from the input field of long type, and convert the result to a value of Integer/int type.

T he input data will be transformed to output data after being processed in the tMap .

Input table

customer_id account_num
1 87462024688
2 87514054179

Output table

customer_id account_num
1 8746
2 8751
Calling a Talend Routine

You can call a Talend Routine in the Expression Builder, you can call a system routine function Numeric.sequence("s1",1,1) to generate a sequence number for each row.

If/else statement

In the Expression Builder, the if / else statement can be written as follows:

condition?value if true:value if false

You can perform a null test before calling a Java method, otherwise it will throw a null pointer exception if the input data contains a null value. For example:


You can also write a nested statement. For example, use the following expression to retrieve the new salary for each employee based on his/her original salary.

Filter Expressions

In the tMap , you can click the filter button and write a filter expression to filter the output data, as shown below:

If there are multiple conditions, you need to use the logical operators (AND, OR) to combine multiple conditions. For example:

AND operator: all conditions should be satisfied.


In this example, the postal_code should not be null AND the gender should be F.

OR operator: one condition should be satisfied."CN")||"FR")||"US")

In this example, the country should be one of CN, FR or US.