Issues using multiple custom type handlers

[Thomas Stallon]

A very common use case:

Suppose there's an entity called "MyEntity.java" like this.

There's three typical attributes in it. An objectA, an objectB, and a list of objectA. I need to serialize them all as a json format into the database, which means that I have to define my own type handler, as below.

But now there's a conflict.

I have to set the @MappedTypes for my type handlers, as Jackson needs the type-reference to which it deserializes into, and when Mybatis instantiates the type handlers, it just assigns to the generic with the classes defined in @MappedTypes.value one by one, which means that value wrote afterwards would overwrite those wrote forwards. 

That is, for example, ALL_TYPE_HANDLER_MAP will only persist MyObjectTypeHandler<ObjectB> for class name "MyObjectTypeHandler", which means that I cannot use MyObjectTypeHandler for attribute objectA manually.

Meanwhile, in map TYPE_HANDLER_MAP, MyListTypeHandler<ObjectA> overwrites MyObjectTypeHandler<ObjectA> with key "ObjectA", which means that I cannot use MyObjectTypeHandler for attribute objectA automatically.

Codes shown below.

[Thomas Stallon]

Edit: there's some bugs in MyEntityDAO.xml, but they has nothing to do with the issue.

2021年2月1日月曜日 16:15:16 UTC+8 Thomas Stallon:

[Guy Rouillier]

Without spending a lot of time with the code you provided, an apparent simple solution would be to just provide a separate TypeHandler for ObjectA an ObjectB.  Perhaps not as elegant as using generics, but gets you where you want to go.

--

Guy Rouillier

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[Thomas Stallon]

Yeah that's an apparent solution, but quite ugly because in a big project, there's tens of thousands of json Objects, and I have to write separate type handlers for them all. That doesn't cost much to code ( as I can extends the same MyBaseJsonTypeHandler.class), but surely increase the numbers of classes by a lot.

2021年2月1日月曜日 17:13:59 UTC+8 Guy Rouillier: