About the database error in the program "Parent not Found"

1. The front-end interface contains a popup box with a parent-child relationship that is not properly called in the subclass, please look at the program

2. When the database corresponds to a table mapping, a field has been mapped to a table in the table, but later manually changed the field to map to table B, and after the update mapping is started, run an error "Parent not found".

Because this operation changes the field mapping table in the database without updating the operation in the map, it generates a new foreign key relationship, where the conflicting foreign keys need to be found in the database and manually removed

3 when the program is running, the field data contains null, which can also cause this error

Note: If the string is made up of concatenation, it can also cause a failure if it contains null

-------above for individual currently encountered error "parent category not Found" reason, with follow-up perfect

About the database error in the program "Parent not Found"