python - Django autoincrement IntergerField by rule -

-

i have special case, customer requires specific (legacy) format of booking numbers, first 1 starts current year: 2015-12345 every year have start 0

the other 1 starting foreign-key: 7-123 first document created every user gets number 1, , on.

unfortunately there long lists starting booking number, fetching records , calculating booking number not option. have thought overriding save() method, reading , auto-incrementing manually, simultaneous inserts?

the best , reliable way sql trigger eliminate worries simultaneous inserts. overriding save method workable.

explicitly declare primary key field , choose integer it. in save method if primary key none means saving new record, query database determine should new primary key, asign , save. wherever call save method need have atomic transaction , retry save if fails.

btw, starting 0 each year. that's going leading conflicts. have prefix primary key year , strip out @ time display it. (believe me don't want mess composite primary keys in django)


Comments

Post a Comment

Popular posts from this blog

mysql - FireDac error 314 - but DLLs are in program directory -

-
i getting when trying access mysql database : [firedac][phys][mysql]-314. cannot load vendor library [libmysql.dll or libmysqlld.dll] this did not happen (unchanged) code, however, have upgraded windows 10 , had reinstall delphi xe8, system configuration matter. in order try solve problem, copied both of files c:\windows\sysytem32. when did not seem work, copied them \win32\debug, generated .exe resides. i imagine doing rather stupid, can't see what. the proper solution place driver file (eg., libmysql.dll ) in application's folder, or place installation location in fddrivers.ini file: [mysql] vendor=<folder>\libmysql.dll (recent versions of documentation seem use vendorlib instead of vendor in ini file.) see rad studio documentation topics configuring drivers (firedac) , connect mysql server (firedac) more information.
Read more

git - How to list all releases of public repository with GitHub API V3 -

-
so per documentation https://developer.github.com/v3/repos/releases/#list-releases-for-a-repository get /repos/:owner/:repo/releases should list relases , https://api.github.com/repos/jquery/jquery/releases should list releases in jquery project , not , why ? because repository doesn't have releases. has tags github presenting in releases page. for more clear example, see: https://github.com/hashicorp/terraform/releases which has both releases , tags showing on page, api shows releases: https://api.github.com/repos/hashicorp/terraform/releases
Read more

c++ - Getting C2512 "no default constructor" for `ClassA` error on the first parentheses of constructor for `ClassB`? -

-
my situation follows. let there header file classdeclarations.h , have following classes declared: class classa; class classb; class classa { public: classa(int x); classa(double y); int returninteger(void) { return m_x; } double returndouble(void) { return m_y; } private: int m_x; double m_y; } class classb { public: classb(int x); int returninteger(void) { return m_x; } private: int m_x; classa m_instancea_1; } let there *.cpp file called classdefns.cpp , define methods of classes declared in classdeclarations.h : #include classdeclarations.h classa::classa(int x) : m_x(x) { } classa::classa(double y) : m_y(y) { } classb::classb(int x) : m_x(x) { // line build error occurs m_instancea_1 = classa(0); } note have commented line compiler says there error: error c2512: 'classa' : no appropriate default constructor avai...
Read more