我试图在30秒后使一个子文档过期。到目前为止，我所做的任何尝试都没有任何效果。
我尝试了：

const productSchema = new mongoose.Schema({
    name: { 
        type: String
    },
    reports: [ReportSchema]
})

mongoose.model('Product', productSchema);

const reportSchema = new mongoose.Schema({   
    title: {
        type: String,
    },
    createdAt: { 
        type: Date,
        expires: 30
    },
});

还尝试：

const reportSchema = new mongoose.Schema({   
    title: {
        type: String,
    },
    createdAt: { type: Date,  expires: 30 }
});

还尝试：

reportSchema.index({ createdAt: 1 }, { expireAfterSeconds: 30 });