为mongoose中的字段设置严格值

我想在mongoose中为字段设置严格值，例如在bellow模式中

var Option_Sets = new Schema({
    setId: {
        type: mongoose.Schema.ObjectId,
        default: mongoose.Types.ObjectId,
        required: true,
        dropDups: true,
        index: true
    },
    setName: { type: String },
    scope: String,
    components: [Schema.Types.Mixed]
});

我想设置范围字段，以便在范围数组中只能取一个

var scopes = ["Global", "Store View", "Website"]; 

请有人帮我举个例子，指导我怎么做。

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要执行此尝试枚举，请提前致谢：

var Option_Sets = new Schema({
    setId: {
        type: mongoose.Schema.ObjectId,
        default: mongoose.Types.ObjectId,
        required: true,
        dropDups: true,
        index: true
    },
    setName: { type: String },
    scope: {
        type: String,
        enum: ["Global", "Store View", "Website"]
    },
    components: [Schema.Types.Mixed]
});

---

要执行此尝试枚举，请执行以下操作：

var Option_Sets = new Schema({
    setId: {
        type: mongoose.Schema.ObjectId,
        default: mongoose.Types.ObjectId,
        required: true,
        dropDups: true,
        index: true
    },
    setName: { type: String },
    scope: {
        type: String,
        enum: ["Global", "Store View", "Website"]
    },
    components: [Schema.Types.Mixed]
});

---

非常感谢…@B，SiscanuThank非常感谢…@B，Siscanu