双点运算符调用了mutator方法来设置每个地址属性的值。

The double-dot operator invokes mutator methods to set values for each of the address attributes.

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为了实现这个目标，我们将调用observer方法(使用双点运算符)获取address列中的结构化类型值的城市属性。(清单2)。

To do that, we will invoke the observer method (using the double-dot operator) for the city attribute of the structured type value in the ADDRESS column (Listing 2).

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