4

我正在用 sqlite-net 做 WP8。有时我希望在不每次都定义表模型的情况下进行原始查询。

我所做的是在下面进行查询，并尝试获取其属性：

    string query = "SELECT firstname, lastname FROM users";

    var records = db.Query<object>(query).ToList();
    foreach (var r in records)
     {
 System.Diagnostics.Debug.WriteLine(r.GetType().GetProperty("firstname").GetValue(r,null).toString());
     }

但是，会发生“System.NullReferenceException”异常。

我可以知道如何在不声明表模型的情况下实际获得值吗？

4

3 回答 3

1

您可以通过这种方式扩展部分类：

namespace SQLite
{
public partial class SQLiteConnection 
{
    public List<object[]> CustomQuery(string query, params object[] args)
    {
        var cmd = CreateCommand(query, args);
        return cmd.ExecuteCustomQuery();
    }
}
public partial class SQLiteCommand
{
    public List<object[]> ExecuteCustomQuery()
    {
        if (SQLiteConnection.Trace)
        {
            Debug.WriteLine("Executing Query: " + this);
        }

        var stmt = Prepare();
        try
        {
            var colLenght = SQLite3.ColumnCount(stmt);

            var lstRes = new List<object[]>();
            while (SQLite3.Step(stmt) == SQLite3.Result.Row)
            {
                var obj = new object[colLenght];
                lstRes.Add(obj);
                for (int i = 0; i < colLenght; i++)
                {
                    var colType = SQLite3.ColumnType(stmt, i);
                    switch (colType)
                    {
                        case SQLite3.ColType.Blob:
                            obj[i] = SQLite3.ColumnBlob(stmt, i);
                            break;
                        case SQLite3.ColType.Float:
                            obj[i] = SQLite3.ColumnDouble(stmt, i);
                            break;
                        case SQLite3.ColType.Integer:
                            obj[i] = SQLite3.ColumnInt(stmt, i);
                            break;
                        case SQLite3.ColType.Null:
                            obj[i] = null;
                            break;
                        case SQLite3.ColType.Text:
                            obj[i] = SQLite3.ColumnString(stmt, i);
                            break;
                    }
                }
            }
            return lstRes;
        }
        finally
        {
            SQLite3.Finalize(stmt);
        }
    }
}
}

在你有一个返回对象数组列表的方法之后，你可以通过这种方式调用：

var query = "select c.Id, c.Name, (select count(*) from Products where IdCategory = c.Id)  from Categories c order by c.Name";
var lst = this.SqlConn.CustomQuery(query);
return (from s in lst
        select new CategoryDescriptor { 
            Id = (int) s[0], 
            Name = (string) s[1], 
            ProductsCount = (int) s[2] 
        });
于 2014-04-09T17:11:16.680 回答
1

简单地：

string query = "SELECT firstname, lastname FROM users";
Statement stQuery = SQLite3.Prepare2(connection.Handle, query);
while ((SQLite3.Result result = SQLite3.Step(stQuery)) == SQLite3.Result.Row)
{
//your stuff here
}
SQLite3.Finalize(stQuery);
于 2014-03-06T12:31:41.267 回答
1

使用前两个答案（第一个答案需要更改源代码，第二个答案不完整）

我想出了这个方法：

    public List<object[]> RunSql(string sqlString, bool includeColumnNamesAsFirstRow)
    {
        var lstRes = new List<object[]>();
        SQLitePCL.sqlite3_stmt stQuery = null;
        try
        {
            stQuery = SQLite3.Prepare2(fieldStrikeDatabase.Connection.Handle, sqlString);
            var colLenght = SQLite3.ColumnCount(stQuery);

            if (includeColumnNamesAsFirstRow)
            {
                var obj = new object[colLenght];
                lstRes.Add(obj);
                for (int i = 0; i < colLenght; i++)
                {
                    obj[i] = SQLite3.ColumnName(stQuery, i);
                }
            }

            while (SQLite3.Step(stQuery) == SQLite3.Result.Row)
            {
                var obj = new object[colLenght];
                lstRes.Add(obj);
                for (int i = 0; i < colLenght; i++)
                {
                    var colType = SQLite3.ColumnType(stQuery, i);
                    switch (colType)
                    {
                        case SQLite3.ColType.Blob:
                            obj[i] = SQLite3.ColumnBlob(stQuery, i);
                            break;
                        case SQLite3.ColType.Float:
                            obj[i] = SQLite3.ColumnDouble(stQuery, i);
                            break;
                        case SQLite3.ColType.Integer:
                            obj[i] = SQLite3.ColumnInt(stQuery, i);
                            break;
                        case SQLite3.ColType.Null:
                            obj[i] = null;
                            break;
                        case SQLite3.ColType.Text:
                            obj[i] = SQLite3.ColumnString(stQuery, i);
                            break;
                    }
                }
            }
            return lstRes;
        }
        catch (Exception)
        {
            return null;
        }
        finally
        {
            if (stQuery != null)
            {
                SQLite3.Finalize(stQuery); 
            }
        }
    }
于 2017-03-24T09:14:55.903 回答