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Troubleshoot "Could not create Foreign Key" errors during deployment

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  • When publishing a module you may, in certain situations, encounter the following error:

    Could not create Foreign Key: This may have happened because there are '<EntityAId>' values of entity '<EntityB>' with no corresponding value in entity '<EntityA>', or attribute 'EntityAId' of entity 'EntityB' is creating a circular dependency between entities. Check error log for details.

    You may see it when publishing a module in Service Studio:

    Or also in Service Center when, for example publishing a solution:

    Most common scenarios

    In this guide, we’ll list the most common situations that can lead to this publishing error and how to fix them. The most probably causes will be listed first, so we suggest to troubleshoot in this order.

    No corresponding values

    In order to create a Foreign Key (FK) from one table to another, it’s important that the table where the FK is being created (entity ‘A' of the error) contains only values that exist on the parent table (entity 'B’ of the error). To give you a practical example, imagine the two tables:

    Entity 'A':

    ID User_ID Task
    1 10 Create
    2 11 Review

    Entity 'B':

    ID Username Email
    5 Ruben
    6 Capitao

    If we create the Foreign Key from Entity 'A' column 'User_ID' to point to Entity 'B' column 'ID', we will obtain an error because the existing data in column 'User_ID' contains values that do not exist in the parent table (entity 'B').

    To validate this hypothesis, check the data on the physical tables that the entities are pointing to.

    To resolve the situation, it is necessary to correct the data in the tables such that all values referenced exist in the parent table, by either:

    • removing entries that do not exist
    • adding the values to the parent table

    Circular dependencies or multiple cascade paths

    It is possible to set up your tables so that when deleting an entry from a table, all foreign keys depending on that entry will also be deleted: this is called cascade deletion. You can do this in OutSystems by going to the properties of the Foreign Key relationship and selecting "Delete" for the Delete Rule property.

    In some scenarios, these delete rules run into scenarios that the database engine cannot handle and therefore does not allow. In the scenarios below, this error is expected and the delete rules should be reviewed to avoid running into the error.

    Circular dependencies

    In the entity diagram above, on the left, the Delete Rules loop back to the table being deleted, which would cause the database engine to follow the delete cascade path indefinitely. Since this would result in undesirable behaviors, the topology of the entity model should be reviewed such that either:

    • one of the Foreign Key relationships does not exist
    • one of the delete rules is not “Delete”

    Multiple cascade paths

    In the entity diagram above, on the right, deleting a value from table X will ultimately cause the deletion of values in table Z, however, the database engine cannot determine which deletion should be made first: Y and consequently Z or directly Z. To avoid this situation, one of the Foreign Key relationships leading to Z should be set to “Ignore”.

    Database timeout

    Considering that the SQL engine validates the data present in the tables, if the tables exist, the larger their size the more time it’s required to create the FK. Validate if the tables have a large number of records and, in that case, update the timeout value in the configuration tool.

    Otherwise, if increasing the timeout is not enough and/or the tables are small, check for database locks.

    Database locks

    It is also possible that locks in the tables prevent the foreign key from being created by simply causing a timeout as described above. In Oracle, you might even see the following error in the event of a lock:

    ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired

    To check if this is the case, you should work with your Database Administrator to determine if there are locks that affect the publish operation and how to resolve them.

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