SQLite System.NotSupportedException：不知道如何阅读 <T>答案

【问题标题】：SQLite System.NotSupportedException: Don't know how to read <T>SQLite System.NotSupportedException：不知道如何阅读 <T>
【发布时间】：2018-12-03 18:33:27
【问题描述】：

我使用 Xamarin Forms 和 Sqlite 开发应用程序。我使用以下 nugets：

sqlite-net-pcl
SQLiteNetExtensions

我想用 sql 创建查询。

我有两张桌子：

CREATE TABLE `AuditFormDto` (
    `AuditDtoGuid`  varchar,
    `Id`    integer NOT NULL PRIMARY KEY AUTOINCREMENT,
    `Guid`  varchar,
    `AuditFormTradePointDtoId`  integer,
    `CreationLocationJson`  varchar,
    `CompletionLocationJson`    varchar,
    `CreationDate`  bigint,
    `CompletionDate`    bigint,
    `Status`    integer,
    `PlaceInAudit`  integer,
    `CreatorId` varchar,
    `ServerId`  integer,
    `AuditServerId` integer,
    `ShouldSync`    integer,
    `Deleted`   integer
);

和

CREATE TABLE `AuditDto` (
    `CreatorId` varchar,
    `RegularQuestionIdsBlobbed` varchar,
    `CreationLocationJson`  varchar,
    `CompletionLocationJson`    varchar,
    `Guid`  varchar NOT NULL,
    `DateCreated`   bigint,
    `DateFinished`  bigint,
    `Name`  varchar,
    `Comment`   varchar,
    `Type`  integer,
    `Status`    integer,
    `ServerId`  integer,
    `ShouldSync`    integer,
    PRIMARY KEY(`Guid`)
);

我还创建了包装类

public class JoinedClass 
{
    public string AuditDtoGuid { get; set; }
    public int Id { get; set; }
    public int Type { get; set; }
    public string Guid { get; set; }
}

但是当我尝试执行这段代码时：

public async Task<JoinedClass> Get(int id)
{
    var strQuery = $"SELECT * FROM AuditFormDto INNER JOIN AuditDto ON  AuditDto.Guid = AuditFormDto.AuditDtoGuid where AuditFormDto.Id = {id}";
    var joinedClass = await _connection.ExecuteScalarAsync<JoinedClass>(strQuery);
    return joinedClass;
}

我有这个例外：

System.NotSupportedException: Don't know how to read JoinedClass

【问题讨论】：

标签： c# .net sqlite xamarin.forms

【解决方案1】：

ExecuteScalarAsync 返回影响的计数而不是行结果。

您可以使用QueryAsync进行更改。

看起来像：

public async Task<IEnumerable<JoinedClass>> Get(int id)
{
    var strQuery = $"SELECT * FROM AuditFormDto INNER JOIN AuditDto ON  AuditDto.Guid = AuditFormDto.AuditDtoGuid where AuditFormDto.Id = {id}";
    var joinedClass = await _connection.QueryAsync<JoinedClass>(strQuery);
    return joinedClass;
}

【讨论】：

什么是异常消息。看图片它工作正常。