使用Dapper映射到嵌套对象不起作用

Question

The Problem

Simply put, the mapping does not perform as expected. The local variable reason comes back as null so the assignment to nav sets the nested object Reason to null as well.

Am I missing something simple here?

The Stored Procedure

ALTER PROCEDURE [PA].[spGetDocumentNavById]
-- Add the parameters for the stored procedure here
@DocumentNavID INT
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;

-- Insert statements for procedure here
SELECT
    dn.DocumentNavID,
    dn.IssuerName,
    nt.Name,
    dn.Amount,
    dn.BTF,
    dn.NavDate,
    dn.ReceivedDate,
    dn.PrimaryIdentifier,
    dn.AssetID,
    dh.LastModifiedBy,
    dh.IsApproved,
    dh.Corrected,
    dh.ReasonID
FROM PA.DocumentNavs dn WITH(NOLOCK)
    JOIN PA.NAVTypes nt WITH(NOLOCK)
        ON nt.NAVTypeID = dn.NavTypeID
    LEFT JOIN PA.DocumentsHistory dh WITH(NOLOCK)
        ON dh.DocumentID = dn.DocumentID
    LEFT JOIN PA.Analysts a WITH(NOLOCK)
        ON a.AnalystID = dh.LastModifiedBy
WHERE dn.DocumentNavID = @DocumentNavID

The C#

public DocumentNav FindById(int documentNavId)
    {
        var data = new
        {
            documentNavId
        };

        using (var conn = SqlConnection)
        {
            var response = conn.Query<DocumentNav, Reason, DocumentNav>("[PA].spGetDocumentNavById",
                map: (nav, reason) =>
                {
                    nav.Reason = reason;
                    return nav;
                }, param: data, splitOn: "ReasonID", commandType: System.Data.CommandType.StoredProcedure)
                .DefaultIfEmpty().FirstOrDefault();

            return response;
        }
    }

Answer 1

Dapper is able to split the returned row query by Id columns ("Id" or "id"). If your primary key is different or you would like to split the row at a point other than Id, use the optional "splitOn" parameter.
In your example the query should look like:

SELECT
    -- DocumentNav Object Columns 
    dn.DocumentNavID AS "Id",
    dn.IssuerName,
    -- ... all other DocumentNav properties..
    -- Reason Object Columns
    dh.ReasonID AS "Id"
    dh.LastModifiedBy,
    dh.IsApproved,
    dh.Corrected
    -- ... all other Reason properties..
FROM PA.DocumentNavs dn WITH(NOLOCK)
    JOIN PA.NAVTypes nt WITH(NOLOCK)
        ON nt.NAVTypeID = dn.NavTypeID
    LEFT JOIN PA.DocumentsHistory dh WITH(NOLOCK)
        ON dh.DocumentID = dn.DocumentID
    LEFT JOIN PA.Analysts a WITH(NOLOCK)
        ON a.AnalystID = dh.LastModifiedBy
WHERE dn.DocumentNavID = @DocumentNavID

You need your objects to be with property name "Id" (DocumentNav & Reason)