猫鼬中的MissingSchemaError

我的架构:

const facultySchema = new Schema({
    title: {
        type: String,
        required: true
    },
    groups: [{
        type: Schema.Types.ObjectId,
        ref: 'Group'
    }]
})

export default model('Faculty', facultySchema)

const groupSchema = new Schema({
    title: {
        type: String,
        required: true
    },
    students: [{
        type: Schema.Types.ObjectId,
        ref: 'Student',
    }],
    journals: [{
        type: Schema.Types.ObjectId,
        ref: 'Journal'
    }]
})

export default model('Group', groupSchema)

这是我的服务,我有错误MissingSchemaError:尚未为模型“Group”注册架构。当我尝试填充组时发生了此错误

class FacultyService {
    getFaculties = async () => {

        const faculties = await Faculty.find().populate('groups')

        if(!faculties) return null

        return faculties
    }
}

export const facultyService = new FacultyService()

当我将代码const gr=wait Group.find()添加到我的getFaculties函数中时,错误消失了。