无法读取存在的值

Question

我正在制作图书馆管理软件.我有一个获取书籍信息的方法:

public static Book GetInfoAboutBook(string title)
    {
        using (SqliteConnection db = new SqliteConnection("Filename=" + fileName))
        {
            db.Open();

            Book b = new Book();

            SqliteCommand sqliteCommand = new SqliteCommand
            {
                Connection = db,
                CommandText = "select Title, Author, Publisher, ISBN, Quantity, CoverImageLocation, Tags from MyBooks where Title = '@Title'",
            };

            sqliteCommand.Parameters.AddWithValue("@Title", title);

            SqliteDataReader query = sqliteCommand.ExecuteReader();

            if(query.Read())
            {
                b.Title = query.GetString(0);
                b.Author = query.GetString(1);
                b.Publisher = query.GetString(2);
                b.Quantity = query.GetInt32(3);
                b.CoverImageLocation = query.GetString(4);
                b.Tags = query.GetString(5);
            }

            return b;
        }
    }

无论输入是什么,'b'都不会被初始化.我确保所有输入实际上都存在于数据库中.但它不起作用.我调试了这个函数.query.Read()永远不会成功.这就是书对象保持为空的方式.这是Book类:

public class Book
{
    public string Title { get; set; }
    public string Author { get; set; }
    public string Publisher { get; set; }
    public string ISBN { get; set; }

    public int Quantity { get; set; }

    public string CoverImageLocation { get; set; }

    public string Tags { get; set; }
}

注意:标题保证是唯一的.

这是数据库的架构:

CREATE TABLE MyBooks(标题文本主键,作者文本不为空,发布者文本不为空,ISBN文本不为空,数量int不为空,CoverImageLocation文本不为空,标签文本不为空);

Answer 1

问题出在你的SQL中:

select Title, Author, Publisher, ISBN, Quantity, CoverImageLocation, Tags
from MyBooks where Title = '@Title'

那是在寻找一本字面标题的书@Title- 它不是在寻找参数值,因为你的@Title引号是文本文字.你想要的SQL:

select Title, Author, Publisher, ISBN, Quantity, CoverImageLocation, Tags
from MyBooks where Title = @Title

差异恰到好处.SQL将@Title在搜索中使用该参数.