mongodb：投影

原創 Lvan-Zhang 2020-05-26 01:09 
db.collection.find(<query>, <projection>)
// <projection>的语法为 { field: inclusion }
// inclusion 1表示返回字段， 0表示不返回字段

不使用投影时，返回符合条件的完整文档，使用投影可以有选择行的返回文档中的部分字段

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