public class User
{
    public int Id { get; set; }
    public string Username { get; set; }
    
    [JsonIgnore] // 这个属性不会被序列化
    public string PasswordHash { get; set; }
}

[DataContract]
public class User
{
    [DataMember]
    public int Id { get; set; }
    
    [DataMember]
    public string Username { get; set; }
    
    [IgnoreDataMember] // 这个属性不会被序列化
    public string PasswordHash { get; set; }
}

public class User
{
    public int Id { get; set; }
    public string Username { get; set; }
    public string PasswordHash { get; set; }
    
    // 当返回false时，PasswordHash不会被序列化
    public bool ShouldSerializePasswordHash() => false;
}

public class CustomContractResolver : DefaultContractResolver
{
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        JsonProperty property = base.CreateProperty(member, memberSerialization);
        
        if (property.PropertyName == "PasswordHash")
        {
            property.ShouldSerialize = _ => false;
        }
        
        return property;
    }
}

// 在Startup.cs中配置
services.AddControllers().AddNewtonsoftJson(options => 
{
    options.SerializerSettings.ContractResolver = new CustomContractResolver();
});

public class UserDto
{
    public int Id { get; set; }
    public string Username { get; set; }
    // 不包含PasswordHash属性
}

public UserDto MapToDto(User user)
{
    return new UserDto
    {
        Id = user.Id,
        Username = user.Username
    };
}