关于实际项目中，对象关联通常是单向还是双向，各有什么优缺点 ？
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Personally, I think this depends on the usage scenario
It is irreversible access, hierarchical relationship, and superior data storage
Can access each other, easy to obtain data
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Personally, I think this depends on the usage scenario
One way
It is irreversible access, hierarchical relationship, and superior data storage
Both directions
Can access each other, easy to obtain data