是否可以通过$ lookup比较带有ObjectId的字符串 [英] Is it possible to compare string with ObjectId via $lookup

问题描述

table1的字段字符串为"value"，而table2的字段值为"value"，为ObjectId，是否可以执行这样的查询或如何编写

table1 has a field string "value" and table2 has a field "value" as ObjectId, Is it possible to do a query like this or how to write

table1.aggregate([
    { 
        $lookup: { 
            from: "table2", 
            localField: "value", 
            foreignField: "_id", 
            as: "test" 
        }  
    }
])

推荐答案

据我所知，在 MongoDB 数据类型中使用$lookup运算符加入集合应该是相同的.如果类型不匹配，则$lookup将不起作用.因此，要加入，您应该使用相同类型的那些字段，因为它会检查平等.

As far I know to join collections using $lookup operator in MongoDB data type should be same. If type mismatch then $lookup will not work. So to join you should use those field that are same type because it check equality.

$ lookup阶段在 输入带有加入"文档的字段的文档 集合

The $lookup stage does an equality match between a field from the input documents with a field from the documents of the "joined" collection

• 如果 localField 键入object，则 foreignField 应为object

  • If localField type object then foreignField should be object

    如果 localField 键入string，则 foreignField 应该为string

    如果 localField 键入number，则 foreignField 应该为number

    $ lookup文档

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