Add dynamic SQL support for r2dbc

[kfyty]

I want to add dynamic SQL support for r2dbc, just like mybatis. Added the DynamicTemplateProvider interface, although it does not provide a default implementation, it provides a basic implementation. Users can fully implement this function using any third-party template framework, such as enjoy, freemarker, st, and so on.

@schauder do you have chance to take a look ?

[mp911de]

Any SQL execution should be performed through the Template API instead of introducing another abstraction for query methods. It would make much more sense to explore how to encapsulate operations from the Repository to invoke a Template-based approach. Right now, operations use PreparedOperation where mapping happens to some extent in R2dbcQueryCreator.

[kfyty]

I think many developers prefer to write SQL directly instead of using template APIs. In addition, currently there is still a lot of development space for template APIs

[mp911de]

Using SQL queries is already possible via @Query so there's nothing that would prevent you from providing SQL yourself.

[kfyty]

Yes, but I need to execute different SQL statements based on the conditions, such as adding mobile number filtering conditions when the parameter has a mobile number. I tried using spel, but it does not support control commands such as if else for. Moreover, the parameter binding of r2dbc is very strict, requiring strict consistency between SQL parameters and interface parameters, otherwise exceptions will occur. For example, if the SQL placeholder has a # {id}, and the interface method has an id and paging parameters, the call to the interface method will fail.

[holmofy]

@kfyty You can try using the spring-data-criteria library