* adds find_with_linked test
* WIP(related test)
* mock related test done
* complete relation test
* loader update
* find_with/also_related missing test case for empty from other side
* comments fixup
* revert loader test
* related select test done
* find with/also linked test cases
* removed due to it being functionally same as the new one
* fmt, remove excess import
* improved model generation
* issue related test case #1790
* added loader test cases and slight improvement to find_related/linked
* miscellaneous changes
* added empty insert, merge load_one test case
* completed loader many to many test case, fmt
* removed empty_insert test case for now
* commented insert_test
* added Cargo.toml for issue 1790's folder
* buffed salvo version for ci(0.49 yanked)
* revert version for salvo example
* Added enum for SQL Error and basic functions for it
* fmt
* Restructured code to allow multiple database system simultaneously
* updated code error and moved Eq to derive by compiler
* added ForeignKeyViolation implementation
* fmt
* added type param
* changed type param and used unwrap_or_default instead of unwrap
* fmt
* refactor code and update documentation
* updated some error code and fixed formatting
* create SQL Err test for UniqueConstraintViolation
* fmt
* updated error codes for mysql errors
* added test for ForeignKeyConstraintViolation and removed unused imports/codes
* fmt
* updated doc and error message
* added static str in SqlErr
* changed to add error message into SqlErr as String
* updated test file to check database type through connection
* fmt
* updated test for SqlErr to match the error type only
* Removed comment and fixed grammar mistake
* fmt
* Update src/error.rs
* Refactoring
---------
Co-authored-by: Chris Tsang <chris.2y3@outlook.com>
Co-authored-by: Billy Chan <ccw.billy.123@gmail.com>
