Question

当使用ExtractYear（）进行简单的算术运算时，django似乎无法创建正确的MySQL查询。

我有一个带有两个数据字段的模型：

class Event(models.Model):
    start_date = models.DateField()
    finish_date = models.DateField()

如果我想查找所有行，以使start_date和finish_date的年份相等，则可以这样做：

from django.db.models import F
from django.db.models.functions import ExtractYear
>>> print Event.objects.annotate(year=ExtractYear(F('start_date'))).filter(finish_date__year=F('year')).only('pk').query
SELECT `event`.`id`, EXTRACT(YEAR FROM `event`.`start_date`) AS `year` FROM `event` WHERE EXTRACT(YEAR FROM `event`.`finish_date`) = (EXTRACT(YEAR FROM `event`.`start_date`))

但是，如果我想查找在随后的几年中开始和结束的事件，请尝试使用以下过滤器，它给我一个不正确的MySQL查询：

>>> print Event.objects.annotate(year=ExtractYear(F('start_date'))).filter(finish_date__year=F('year')+1).only('pk').query
SELECT `event`.`id`, EXTRACT(YEAR FROM `event`.`start_date`) AS `year` FROM `event` WHERE `event`.`finish_date` BETWEEN 0001-01-01 AND 0001-12-31

我尝试将F('year')+1替换为F('year')+Value(1)，但没有帮助。

我在某个地方错了吗，还是看起来像是Django中的错误？
如果您看到其他方法可以做到这一点，我也将不胜感激！

Answer 1

查询似乎合法。

但是，在我的情况下，另一个查询有效：

Event.objects.annotate(s_year=ExtractYear(F('start_date')), f_year=ExtractYear(F('finish_date')), diff=F("f_year")-F("s_year")).filter(diff=1).only('pk')

只需标注开始日期，完成日期和差异。

Answer 2

这终于奏效了：

public sealed class Client
{
    private string username = "";
    private string _platform = "";
    private readonly HubConnection _connection;
    private readonly IHubProxy _proxy;

    public string _Username
    {
        get { return username; }
        set { username = value; }
    }

    public string _Platform
    {
        get { return _platform; }
        set { _platform = value; }
    }

    public event EventHandler<string> OnMessageReceived;
    public static Client instance = null;

    public Client(string name, string username, string firstname, string lastname, string company, string department, string section)
    {
        _Username = username;
        _Platform = name;
        _platform = _Platform;

        Dictionary<string, string> queryString = new Dictionary<string, string>();
        queryString.Add("username", username);
        queryString.Add("firstname", firstname);
        queryString.Add("lastname", lastname);
        queryString.Add("company", company);
        queryString.Add("department", department);
        queryString.Add("section", section);

        _connection = new HubConnection("https://www.example.com/SignalRhub",queryString );

        _proxy = _connection.CreateHubProxy("chathub");
    }

    public static Client Getinstance(string name, string username, string firstname, string lastname)
    {
        // create the instance only if the instance is null
        if (instance == null)
        {
            // The username and user's name are set before instantiation
            instance = new Client(name, username, firstname, lastname,"","","");
        }
        // Otherwise return the already existing instance
        return instance;
    }
    public async Task Connect()
    {

        await _connection.Start(); //.ContinueWith._connection.server.registerMeAs("");
        _proxy.On("broadcastMessage", (string platform, string message) =>
        {
            if (OnMessageReceived != null)
                OnMessageReceived(this, string.Format("{0}: {1}", platform, message));
        });

    }

    public async Task<List<string>> ConnectedUsers()
    {

        List<string> Users = await _proxy.Invoke<List<string>>("getConnectedUsers");

        return Users;
    }

    public async Task<List<string>> ConnectedDeptUsers(string company, string dept, string section, string username)
    {

        List<string> Users = await _proxy.Invoke<List<string>>("getConnectedTeamUsers",company, dept, section, username);

        return Users;
    }

    public Task Send(string message)
    {
        return _proxy.Invoke("Send", _platform, message);
    }

    public Task SendTeamMessage(string company, string dept, string section, string name, string message)
    {
        return _proxy.Invoke("messageTeam", company,  dept,  section,  name,  message);
    }

    public Task SendCompanyMessage(string company, string dept, string section, string name, string message)
    {
        return _proxy.Invoke("messageCompany", company, dept, message);
    }
}

好像django中有一个错误。我将其添加到https://code.djangoproject.com/ticket/30494中。

查询中带有年份的算术表达式问题

2 个答案: