Today, a back-end system project suddenly start being given, later found the wrong point in accordance with an error console, manually change the return type Integer no problem
However, because the project has been in use, the problem has not yesterday, then go online to find the cause of the error bit
错误信息：Could not write JSON: (was java.lang.NullPointerException); nested exception is com.fasterxml.jackson.databind.JsonMappingException
Entity class data type does not match the value of the package! !
Means an entity class and type of the attribute type set / get his method of generating different, such properties are the basis of the type of packaging, types of set / get the method is a base class that will BUG, and vice versa
Today in remote debugging someone else's project met problems when a database, you need to delete the two foreign key constraint table with each other, the Internet to find instructions to delete the foreign key constraint
SET FOREIGN_KEY_CHECKS=0;
After using manually delete the table still not afford to delete, and then find another more detailed Gangster blog, the new inquiry directly to run these three can delete the table from each other constraints, and so, the problem is solved
1 SET FOREIGN_KEY_CHECKS = 0; // foreign key constraint cancel
a table 2 drop table therein;
. 3 = FOREIGN_KEY_CHECKS the SET. 1; // add foreign key constraint