使用Codable协议解析多层嵌套数组时遇解码错误

Let's break down what's happening here: that error means somewhere in your Codable model definitions, you've declared a property as an array type (like [SomeType]), but the API is returning a single dictionary (object) at that position. Looking at your sample response, the entire top-level structure is a dictionary (not an array), and the only array lives under Students.Enrollments.

Step 1: Define Correct Codable Models #

You need to create structs that mirror the exact hierarchy of your API response. Here's how to model it properly:

// Top-level response model that holds both FatherModel and Students
struct ParentStudentResponse: Codable {
    let fatherModel: FatherModel
    let students: Students
    
    // Map snake_case API keys to camelCase Swift properties
    enum CodingKeys: String, CodingKey {
        case fatherModel = "FatherModel"
        case students = "Students"
    }
}

struct FatherModel: Codable {
    let userId: Int
    let parentType: String
    let partnerId: Int
    let educationId: Int
    let user: User
    
    enum CodingKeys: String, CodingKey {
        case userId = "UserId"
        case parentType = "ParentType"
        case partnerId = "PartnerId"
        case educationId = "EducationId"
        case user = "User"
    }
}

struct User: Codable {
    let id: Int
    let firstName: String
    let lastName: String
    
    enum CodingKeys: String, CodingKey {
        case id = "Id"
        case firstName = "FirstName"
        case lastName = "LastName"
    }
}

struct Students: Codable {
    let id: Int
    let enrollments: [Enrollment]
    
    enum CodingKeys: String, CodingKey {
        case id = "Id"
        case enrollments = "Enrollments"
    }
}

struct Enrollment: Codable {
    let id: Int
    let studentId: Int
    let classId: Int
    
    enum CodingKeys: String, CodingKey {
        case id = "Id"
        case studentId = "StudentId"
        case classId = "ClassId"
    }
}

Step 2: Decode the Response #

Once your models are set up correctly, you can decode the data like this:

// Assume you have your API response data stored in the 'data' variable
do {
    let decoder = JSONDecoder()
    let response = try decoder.decode(ParentStudentResponse.self, from: data)
    
    // Access your decoded data here
    print("Father's full name: \(response.fatherModel.user.firstName) \(response.fatherModel.user.lastName)")
    if let firstEnrollment = response.students.enrollments.first {
        print("First enrollment ID: \(firstEnrollment.id)")
    }
} catch {
    print("Decoding failed: \(error.localizedDescription)")
    // For more detailed debugging, print the full error
    print("Full error details: \(error)")
}

Common Mistakes to Avoid #

• Top-level array mismatch: The biggest culprit is usually trying to decode [FatherModel].self or [Students].self directly—your API returns a single dictionary containing both models, not an array of either.
• Nested type mismatches: Double-check that properties like fatherModel (a single object) aren't declared as [FatherModel], and that enrollments (the only array in the response) is correctly typed as [Enrollment].
• CodingKeys typos: Ensure your CodingKeys exactly match the case-sensitive key names in the API response (e.g., "FatherModel" vs "fathermodel" will break decoding).

内容的提问来源于stack exchange，提问作者Android teem