Dapper MultiQuery 仅返回第一个匹配项

Question

我有一个查询来获取单个文档：-

SELECT      doc.Id
            ,doc.Type
            ,doc.Name
            ,doc.Description
            ,doc.File
            ,doc.CreatedAt
            ,doc.UpdatedAt
            ,dl.LabelId
            ,l.Name
            ,l.Description
            ,dc.DocumentId
            ,dc.ProfileId
            ,dc.Role
FROM        Documents as doc
LEFT JOIN   DocumentCollaborators as dc
    ON      doc.Id = dc.DocumentId
LEFT JOIN   DocumentLabels as dl
    ON      doc.Id = dl.DocumentId
LEFT JOIN   Labels as l
    ON      dl.LabelId = l.Id
WHERE       doc.Id =  @Id

我用 Dapper 查询这个问题如下：

var documents = await connection.QueryAsync<DocumentDto, LabelDto, CollaboratorDto, DocumentDto>(
            GetDocumentSql,
            (doc, label, collaborator) => {
                if (label.LabelId != Guid.Empty) // empty guid means no label
                {
                    doc.Labels.Add(label);
                }
                if (collaborator.ProfileId != Guid.Empty) // empty guid means no collaborator
                {
                    doc.Collaborators.Add(collaborator);
                }
                return doc;
            }, 
            new
            {
                Id = documentId.ToString()
            },
            splitOn: "LabelId,DocumentId");

我的DTO如下：

public abstract class BaseDocumentDto
{
    public Guid Id { get; set; }
    public int Type { get; set; }
    public string Name { get; set; } = string.Empty;
    public string Description { get; set; } = string.Empty;
    public string File { get; set; } = string.Empty;
    public DateTime CreatedAt { get; set; }
    public DateTime UpdatedAt { get; set; }
}

public class DocumentDto : BaseDocumentDto
{
    public IList<LabelDto> Labels { get; set; } = new List<LabelDto>();
    public IList<CollaboratorDto> Collaborators { get; set; } = new List<CollaboratorDto>();
}

public class LabelDto
{
    public Guid LabelId { get; set; }
    public string Name { get; set; } = string.Empty;
    public string Description { get; set; } = string.Empty;
    public DateTime CreatedAt { get; set; }
    public DateTime UpdatedAt { get; set; }
}

public class CollaboratorDto
{
    public Guid ProfileId { get; set; }
    public int Role { get; set; }
}

如果我尝试在数据库有多个标签或协作者记录的情况下运行此程序，那么我只能得到返回的第一个记录

DocumentDTO

。

我做错了什么？

Answer 1

这是您做错的地方：您假设结果集中第二行中的文档与第一行中的文档相同。事实并非如此，每行都会有一个新的

doc

。相反，这样做：

DocumentDto myDoc = null;
var documents = await connection.QueryAsync<DocumentDto, LabelDto, CollaboratorDto, DocumentDto>(
    GetDocumentSql, (doc, label, collaborator) => 
        {
            if (myDoc is null)
            {
                myDoc = doc;
            }  
            if (label.LabelId != Guid.Empty) // empty guid means no label
            {
                myDoc.Labels.Add(label);
            }
            if (collaborator.ProfileId != Guid.Empty) // empty guid means no collaborator
            {
                myDoc.Collaborators.Add(collaborator);
            }
            return null; // Your data is in myDoc, no need to return anything
        }, 
        new
        {
            Id = documentId.ToString()
        },
        splitOn: "LabelId,DocumentId");
// Go ahead and use myDoc