Realm结合HandyJSON或Codable的坑

一、问题

对于使用HandyJson或Codable来解析的数据转成Realm实例时失败！！！
转成Realm实例时HandyJson自定义映射无效！！！

二、解决方案

1. HandyJson

问题1：

let JsonString = """
{"genres":[{"id":28,"name":"Action"},{"id":12,"name":"Adventure"},{"id":16,"name":"Animation"},{"id":35,"name":"Comedy"},{"id":80,"name":"Crime"},{"id":99,"name":"Documentary"}]}
"""

class Genres: Object, HandyJSON {
    @objc dynamic var id: String = ""
    @objc dynamic var name: String?

    override class func primaryKey() -> String? {
        "id"
    }

    override required init() {
        super.init()
    }
}

let list: [Genres] = ([Genres].deserialize(from: JsonString, designatedPath: "genres") ?? []).compactMap { $0 }
list.forEach { print($0.id, $0.name) }

这里Realm对象的属性不可使用@Persisted标注，应该使用@objc dynamic标注为OC的动态类型。使用HandyJson有个便捷之处是解析时可以直接将id从Int转成String。

问题2：

这里有两种解决思路，直接上代码：

let JsonString = """
{"genres":[{"id":28,"name":"Action"},{"id":12,"name":"Adventure"},{"id":16,"name":"Animation"},{"id":35,"title":"Comedy"},{"id":80,"title":"Crime"},{"id":99,"title":"Documentary"}]}
"""

class Genres: Object, HandyJSON {
    @objc dynamic var id: String = ""
    @objc dynamic var name: String?
    private var title: String?

    override class func primaryKey() -> String? {
        "id"
    }

    override required init() {
        super.init()
    }

    /// 转换完成后赋值
    func didFinishMapping() {
        name = [name, title].compactMap { $0 }.first
    }
}

let list: [Genres] = ([Genres].deserialize(from: JsonString, designatedPath: "genres") ?? []).compactMap { $0 }
list.forEach { print($0.id, $0.name) }

这种方式是在HandyJson的didFinishMapping中直接给属性赋值。再看另一种方式：

let JsonString = """
{"genres":[{"id":28,"name":"Action"},{"id":12,"name":"Adventure"},{"id":16,"name":"Animation"},{"id":35,"title":"Comedy"},{"id":80,"title":"Crime"},{"id":99,"title":"Documentary"}]}
"""

class Genres: Object, HandyJSON {
    @objc dynamic var id: String = ""
    @objc dynamic var name: String?
    @objc private var title: String? {
        willSet {
            name = newValue
        }
    }

    override class func ignoredProperties() -> [String] {
        ["title"]
    }

    override class func primaryKey() -> String? {
        "id"
    }

    override required init() {
        super.init()
    }
}

let list: [Genres] = ([Genres].deserialize(from: JsonString, designatedPath: "genres") ?? []).compactMap { $0 }
list.forEach { print($0.id, $0.name) }

这里需要注意title属性前面加了@objc修饰表示这是OC属性，这样HandyJson在对title赋值时willSet将被调起，我们可以在willSet中对name进行赋值。如果不希望title属性也存储到Realm中，可以在Realm的ignoredProperties方法中标注。

执行代码后可以验证结果：

从Realm的表结构可以看出，只有id和name，title并不存在，其次name的值也是完整的，这也符合我们的预期。

2. Codable

let JsonString = """
{"genres":[{"id":28,"name":"Action"},{"id":12,"name":"Adventure"},{"id":16,"name":"Animation"},{"id":35,"name":"Comedy"},{"id":80,"name":"Crime"},{"id":99,"name":"Documentary"}]}
"""

class GenresModel: Object, Codable {
    @Persisted(primaryKey: true) var id: Int
    @Persisted var name: String?

    override required init() {
        super.init()
    }
}

let list = ([GenresModel].decodeJSON(from: JsonString, designatedPath: "genres") ?? []).compactMap { $0 }
list.forEach { print($0.id, $0.name) }

这里Realm对象的属性可以使用@Persisted标注。使用Codable解析时需要注意匹配数据类型，不可以直接将id从Int转成String，当然你也可以写映射方法来实现。