database design - When/Why to use Cascading in SQL Server? -

-

when setting foreign keys in sql server, under circumstances should have cascade on delete or update, , reasoning behind it?

this applies other databases well.

i'm looking of concrete examples of each scenario, preferably has used them successfully.

summary of i've seen far:

  • some people don't cascading @ all.

cascade delete

  • cascade delete may make sense when semantics of relationship can involve exclusive "is part of" description. example, orderline record part of parent order, , orderlines never shared between multiple orders. if order vanish, orderline should well, , line without order problem.
  • the canonical example cascade delete someobject , someobjectitems, doesn't make sense items record ever exist without corresponding main record.
  • you should not use cascade delete if preserving history or using "soft/logical delete" set deleted bit column 1/true.

cascade update

  • cascade update may make sense when use real key rather surrogate key (identity/autoincrement column) across tables.
  • the canonical example cascade update when have mutable foreign key, username can changed.
  • you should not use cascade update keys identity/autoincrement columns.
  • cascade update best used in conjunction unique constraint.

when use cascading

  • you may want strong confirmation user before allowing operation cascade, depends on application.
  • cascading can trouble if set foreign keys wrong. should okay if right.
  • it's not wise use cascading before understand thoroughly. however, useful feature , therefore worth taking time understand.

Comments

Post a Comment

Popular posts from this blog

c++ - How do I get a multi line tooltip in MFC -

-
right now, have tool tip pops when hover on edit box. problem tool tip contains multiple error messages , in 1 long line. need have each error message on own line. error messages contained in cstring new line seperating them. my existing code below. bool ontooltiptext(uint, nmhdr* pnmhdr, lresult* presult) { assert(pnmhdr->code == ttn_needtexta || pnmhdr->code == ttn_needtextw); // need handle both ansi , unicode versions of message tooltiptexta* pttta = (tooltiptexta*)pnmhdr; tooltiptextw* ptttw = (tooltiptextw*)pnmhdr; // tchar szfulltext[256]; cstring strtiptext=_t(""); uint nid = pnmhdr->idfrom; if (pnmhdr->code == ttn_needtexta && (pttta->uflags & ttf_idishwnd) || pnmhdr->code == ttn_needtextw && (ptttw->uflags & ttf_idishwnd)) { // idfrom hwnd of tool nid = ::getdlgctrlid((hwnd)nid); } //m_errprojaccel[ch] contains 1 or more error messages each...
Read more

asp.net - In javascript how to find the height and width -

-
i having .aspx , masterpage page. in masterpage loading aspx page . in aspx page design using generating table structure using code-behind server in javascript how find height , width . regards, kumar if you're looking table height , width, should it var tbl = document.getelementbyid('tbldemo'); alert(tbl.offsetwidth + '\n' + tbl.offsetheight);
Read more

c# - DataTable to EnumerableRowCollection -

-
i have datatable according client requirement can contain invalid date "00/00/1999",null,empty string.(typed datset) when collect them enumerables wish convert of invalid forms empty string. (i.e) enumerablerowcollection<datarow> query = order in _table.asenumerable() select new { orderdate= string.isnullorempty(convert.tostring(order.field<datetime>("orderdate")) || (how check date invalid date) ? string.empty : order.field<datetime>("orderdate") } how check whether date valid date or not? datetime.tryparse...like given current code: datetime date; enumerablerowcollection<datarow> query = order in _table.asenumerable() select new { orderdate= string.isnullorempty(convert.tostring(order.field<datetime>("orderdate")) || !datetime.tryparse(convert.tostring(order.field<datetime...
Read more