缺少方法异常 Xamarin

Question

我创建了一个具有sqlite连接的xamarin应用程序。 当我运行此代码时，它会导致异常：

public List<string> GetTpe(string word)
{
return dbConnection.Query<string>("Select * From Entries Where Entries.word =?", word).ToList();
}

这是我的班级条目：

public class Entries
{
public Entries()
{
}
public Entries(string word)
{
this.word = word;
}
public Entries(string word, string wordtype, string definition)
{
this.word = word;
this.type = wordtype;
this.defn = definition;
}   
public string word
{ get; set; }
public string type
{ get; set; }
public string sdex { get; set; }
public int wlen { get; set; }
public string defn
{ get; set; }
//public List<string> Word { get; set; }

}

这是例外：System.MissingMethodException：找不到类型"System.String"上的构造函数。

请帮忙。非常感谢。

Answer 1

此 SQL 查询返回的是Entries对象，而不是string。

Query<string>("Select * From Entries Where Entries.word = ?", word)

如果您尝试仅返回string列表，并且该string是记录中的一个字段，则让我们将其分解为组件：

var entriesList = conn.Query<Entries>("Select * From Entries Where Entries.word =?", word);
var stringEnumuerationOfDefn = entriesList.Select(entries => entries.defn);
var stringListOfDefn = stringEnumuerationOfDefn.ToList();

更新：

conn.Insert(new Entries { word = "someWord", defn = "defn1", sdex = "sdex1" });
string wordFilter = "someWord";
var entriesList = conn.Query<Entries>("Select * From Entries Where Entries.word = ? ", word); // new string[1] { word });
var wordEnumueration = entriesList.Select(entries => entries.defn);
var wordList = wordEnumueration.ToList();
foreach (var word in wordList)
{
Console.WriteLine(word)
}