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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 article introduces the syntax to use in the Expression Builder, to help you understand and use the tMap component.
Environment
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.
Description
Mapping 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
tMap provides a graphical tool called Map Editor that allows you to more easily create the mapping from the input table to the output table using a 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 screenshot above, you can see that the format used to map the input column in the Expression Builder of the corresponding output column is rowName.columnName, or 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 |
Note: 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 including 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.
The 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. For example, 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:
row1.Postal_code==null?null:row1.Postal_code.toUpperCase()
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.
row1.salary>=10000?row1.salary*1.05:(row1.salary>=8000?row1.salary*1.1:(row1.salary>=7000?row1.salary*1.08:row1.salary*1.2))
Filter Expressions
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.
row1.postal_code!=null&&row1.gender.equals("F")
In this example, the postal_code should not be null AND the gender should be F.
OR operator: one condition should be satisfied.
row1.country.equals("CN")||row1.country.equals("FR")||row1.country.equals("US")
In this example, the country should be one of CN, FR, or US.
