c# - 具有多个 WHERE 条件的 SQLite 数据库查询

Question

尝试开发 Windows 8.1 商店应用程序。除其他困难外，我还需要在 where 子句上使用两个参数从 sqlite 数据库中检索记录。我可以在 where 子句中使用一个参数成功查询，但是当我尝试使用两个参数时它会崩溃。这是我的代码:

    public string SaveMaint(MaintViewModel Maintenance)
    {
        string result = string.Empty;
        using (var db = new SQLite.SQLiteConnection(App.DBPath))
        {
            string change = string.Empty;
            try
            {
                var existingmaintenance = db.Query<maintenance> ("select * from maintenance where VehID = ? AND MaintID = ?", new String[] {Maintenance.Maintid, Maintenance.Vehicleid});
               // var existingmaintenance = (db.Table<maintenance>().Where 
               //     (c => c.MaintID == Maintenance.Maintid).SingleOrDefault());

                if (existingmaintenance != null)
                {
                    existingmaintenance.VehID = Maintenance.Vehicleid;
                    existingmaintenance.MaintID = Maintenance.Maintid; 
                    existingmaintenance.ServiceDate = Maintenance.Servicedate;
                    existingmaintenance.ServiceCost = Maintenance.Servicecost;
                    existingmaintenance.ServiceLocation = Maintenance.Servicelocation;
                    existingmaintenance.ServiceNote = Maintenance.Servicenote;
                    existingmaintenance.ServiceOdom = Maintenance.Serviceodom;
                    int success = db.Update(existingmaintenance);
                }
                else
                {
                    int success = db.Insert(new maintenance()
                    {
                        VehID = Maintenance.Vehicleid,
                        MaintID = Maintenance.Maintid,
                        ServiceDate = Maintenance.Servicedate,
                        ServiceCost = Maintenance.Servicecost,
                        ServiceLocation = Maintenance.Servicelocation,
                        ServiceNote = Maintenance.Servicenote,
                        ServiceOdom = Maintenance.Serviceodom
                    });
                }
                result = "Success";
            }
            catch
            {
                result = "This project was not saved.";
            }
        }
        return result;
    }

请引用定义existingmaintenance变量的行。此行的注释掉版本工作正常。当我用双参数查询替换变量定义时(使用不同的方法获得，因为我不知道如何向表查询方法添加第二个参数)，它崩溃了。

感谢您提供的任何帮助。抱歉，我只理解了一半我在做什么。

Answer 1

假设您使用的是 SQLite-Net作为你的ORM，你可以在查询后传入参数。据我所知，不支持匿名类，如您的示例所示。试试这个:

var existingmaintenance = db.Query<maintenance>(
    "select * from maintenance where VehID = ? AND MaintID = ?",
    Maintenance.Vehicleid, Maintenance.Maintid).FirstOrDefault();

您还可以使用 linq 查询，如下所示:

var existingmaintenance = db.Table<maintenance>().Where 
    (c => c.VehID == Maintenance.Vehicleid && 
    c.MaintID == Maintenance.Maintid).FirstOrDefault();