Expression to SQL (iii)--Custom function

SQL statements have many functions such as Len (), now (), and so on. How to generate these functions. Recent studies have also written ways to make reference for all.

First, establish an extension class, control can only allow these functions to appear, if there are other functions directly report the exception.

1   Public Static classSqlMethods2     {3          Public Static BOOLDb_in<t> ( ThisT T, list<t> List)//inch4         {5             return true;6         }7          Public StaticBoolean db_notin<t> ( ThisT T, list<t> List)// not in8         {9             return true;Ten         } One          Public Static intDb_length ( This stringT//Len (); A         { -             return 0; -         } the          Public Static BOOLDb_like ( This stringTstringStr// like -         { -             return true; -         } +          Public Static BOOLDb_notlike ( This stringTstringStr// not-like -         { +             return true; A         } at}

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We're going to generate SQL, so the return value of the function is not meant to be, Len (), like, and not only for string types, in and not is for all types.

Two. Handle the logic related to different functions.

1. Determine the namespace of the class in which the function is located I'm asking for it.

2. Processing according to the name of the letter. Unexpected function throw exception occurred

The code reads "

1  Private stringDealmethodscall (methodcallexpression m_exp)2         {3             varK =M_exp;4             varg = k.arguments[0];5             ///The class name where the control function resides. 6             if(K.method.declaringtype! =typeof(sqlmethods))7             {8                 Throw NewException ("function not recognized");9             }Ten             Switch(K.method.name) One             { A                  Case "Db_length": -                     { -                         varExp = k.arguments[0]; the                         return "LEN ("+ dealexpression (exp) +")"; -                     } -                  Case "db_in": -                  Case "Db_notin": +                     { -                         varEXP1 = k.arguments[0]; +                         varEXP2 = k.arguments[1]; A                         stringMethods =string. Empty; at                         if(K.method.name = ="inch") -                         { -Methods ="inch"; -                         } -                         Else -                         { inMethods =" not in"; -                         } to                         returnDealexpression (EXP1) + methods +dealexpression (EXP2); +                     } -                  Case "Db_like": the                  Case "Db_notlike": *                     { $                         varEXP1 = k.arguments[0];Panax Notoginseng                         varEXP2 = k.arguments[1]; -                         stringMethods =string. Empty; the                         if(K.method.name = ="Db_like") +                         { AMethods =" like"; the                         } +                         Else -                         { $Methods =" not-like"; $                         } -                         returnDealexpression (EXP1) + methods +dealexpression (EXP2); -  the                     }  -             }Wuyi             ///Unknown function the             Throw NewException ("Unexpected function"); -}

working with related functions

Three. Debug results

　　

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Expression to SQL (iii)--Custom function