Changes between Version 14 and Version 15 of FDORfc50
- Timestamp:
- 06/03/10 10:11:58 (14 years ago)
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FDORfc50
v14 v15 39 39 * '''Cons''': We add a new command and a new type command, we already have a FdoIExtendedSelect for scrollable readers and users can be confused by those two commands. This will add more complexity in the API. 40 40 41 * Enhance FdoISelect, then create a !FdoSelect base class and add default implementers for !GetFeatureClassNames () and !GetJoinCriteria(). Then each provider would be changed to base their select command implementation on !FdoSelect instead of FdoISelect. Two new capability functions will be added so that applications can determine: if a provider supports the join criteria and supported join types,!SupportsJoins() & !GetJoinTypes(). Again, if future enhancements are ever made to FdoISelect, the need to change each provider would be eliminated.41 * Enhance FdoISelect, add two new methods ‘GetFeatureClassNames()’ and ‘GetJoinCriteria()’. In addition, create an !FdoSelect base class and add default implementers for !GetFeatureClassNames() and !GetJoinCriteria(). Then each provider would be changed to implement their select command implementations on !FdoSelect instead of FdoISelect. Two new capability functions will be added to the FDO FdoIConnectionCapabilities Interface so that applications can determine if a provider supports the join criteria and supported join types. These new capabilites would be named: !SupportsJoins() & !GetJoinTypes(). Again, if future enhancements are ever made to FdoISelect, the need to change each provider would be eliminated. 42 42 * '''Pros''': this solution will not add more complexity to the API.[[BR]] 43 43 * '''Cons''': We need to change all the providers leading to a big effort from everyone. 44 44 45 * Enhance FdoISelect, add two new methods ‘!GetFeatureClassNames()’ and ‘!GetJoinCriteria()’ with a default implementation throwing an exception. Providers which want to implement these new methods just can override then and provide a detailed implementation. Even FdoISelect is declared as ‘interface’ we do not have interfaces in C++ and we can have all other abstract methods and only the new one with a default implementation. A good example here would be locking methods from select command: most of the provider do not support locking and have to provide an empty implementation (usually to throw an exception), so more code on provider side when we could just provide a default implementation in the base class. Following this path we just modify the base class and all other providers will not be changed since will inherit the default implementation. Looking at FdoISelect there are already two methods which provide default implementation: !AddRef() and Release(), so adding default implementation for the new methods will not be something totally new.45 * Enhance FdoISelect, add two new methods ‘!GetFeatureClassNames()’ and ‘!GetJoinCriteria()’ with a default implementation throwing an exception. Providers which want to implement these new methods just can override then and provide a detailed implementation. Even though FdoISelect is declared as ‘interface’ we do not have interfaces in C++ and we can have all other abstract methods and only the new one with a default implementation. A good example here would be locking methods from select command: most of the provider do not support locking and have to provide an empty implementation (usually to throw an exception), so more code on provider side when we could just provide a default implementation in the base class. Following this path we just modify the base class and all other providers will not be changed since will inherit the default implementation. Looking at FdoISelect there are already two methods which provide default implementation: !AddRef() and Release(), so adding default implementation for the new methods will not be something totally new. As with option #2 above: Two new capability functions will be added to the FDO FdoIConnectionCapabilities Interface so that applications can determine if a provider supports the join criteria and supported join types. These new capabilites would be named: !SupportsJoins() & !GetJoinTypes(). 46 46 * '''Pros''': this solution will not add more complexity to the API, we do not need to change any provider.[[BR]] 47 47 * '''Cons''': None. … … 82 82 }}} 83 83 84 We need to define supported cases and all necessary classes need to be added:85 86 84 === Selecting form Multiple Classes === 87 85 … … 89 87 * !FdoIdentifier’s in case we just need to pass a class name. 90 88 * !FdoComputedIdentifier’s having a name and as expression value an !FdoIdentifier, this way we can get aliases, e.g. !PropName AS !NewPropName. We already use computed identifiers in our API for expressions and we provide a name and an expression value. In this case it will be the same, since an alias is actually an expression: we provide an alias (name) and the real name of the property. 91 * !FdoClassComputedIdentifier’s which is a FdoISelect having a name. This option might not be supported by all RDBMS providers and it depends of the internal implementation. This class behaves like a computed class which will be evaluated at run time and really depends of the provider implementation. This new class will help to define sub-selects , see below case (C)89 * !FdoClassComputedIdentifier’s which is a FdoISelect having a name. This option might not be supported by all RDBMS providers and it depends of the internal implementation. This class behaves like a computed class which will be evaluated at run time and really depends of the provider implementation. This new class will help to define sub-selects. Refer to '''Handle Sub-Selects''' below. 92 90 93 91 We will use some SQL examples just to illustrate things we are trying to achieve, each RBDMS-based provider will translate FDO selects in server side SQL depending of the server capabilities.
