In SAP Module Pool programming (Dialog Programming, using ABAP), the concepts of CHAIN and ENDCHAIN are used in screen programming for grouping input fields together when you want to validate or check them collectively.

CHAIN … ENDCHAIN

• It is a block statement in the flow logic of a screen.
• All input fields (screen fields) mentioned between CHAIN and ENDCHAIN are treated as a group.
• Any FIELD validation (such as MODULE <modname> ON CHAIN-REQUEST or MODULE <modname> ON CHAIN-INPUT) applies to the entire group, not just one field.
• If one field in the chain fails validation, all fields in the chain are highlighted.

When to use CHAIN–ENDCHAIN

1. When you want to validate multiple fields together.
   • Example: If the user enters “Start Date” and “End Date”, both fields should be validated together (End Date cannot be earlier than Start Date).
2. When the error message should highlight all fields in the group, not only the one with the issue.
3. When dependencies exist between fields.

PROCESS BEFORE INPUT.
CHAIN.
FIELD v_start_date.
FIELD v_end_date.
MODULE check_dates ON CHAIN-INPUT.
ENDCHAIN.

Key Points

• CHAIN–ENDCHAIN must enclose at least one FIELD statement.

• You use it in PBO/PAI flow logic of a screen (mostly in PAI).

• It is mainly used with:

  • MODULE ... ON CHAIN-INPUT

  • MODULE ... ON CHAIN-REQUEST