Dapper中的自定义映射

Question

我正在尝试使用带有Dapper和多映射的CTE来获取分页结果.我对重复的列感到不便; 例如,CTE阻止我使用Name列.

我想将以下查询映射到以下对象,而不是列名称和属性之间的不匹配.

查询:

WITH TempSites AS(
    SELECT
        [S].[SiteID],
        [S].[Name] AS [SiteName],
        [S].[Description],
        [L].[LocationID],
        [L].[Name] AS [LocationName],
        [L].[Description] AS [LocationDescription],
        [L].[SiteID] AS [LocationSiteID],
        [L].[ReportingID]
    FROM (
        SELECT * FROM [dbo].[Sites] [1_S]
        WHERE [1_S].[StatusID] = 0
        ORDER BY [1_S].[Name]
        OFFSET 10 * (1 - 1) ROWS
        FETCH NEXT 10 ROWS ONLY
    ) S
        LEFT JOIN [dbo].[Locations] [L] ON [S].[SiteID] = [L].[SiteID]
),
MaxItems AS (SELECT COUNT(SiteID) AS MaxItems FROM Sites)

SELECT *
FROM TempSites, MaxItems

对象:

public class Site
{
    public int SiteID { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public List<Location> Locations { get; internal set; }
}

public class Location
{
    public int LocationID { get; set; }
    public string Name { get; set; }
    public string Description { get; set; }
    public Guid ReportingID { get; set; }
    public int SiteID { get; set; }
}

由于某种原因,我在脑海中有一个命名约定,它将为我处理这个场景,但我在文档中找不到它.

Answer 1

有一个以上的问题,让我们一一介绍.

CTE重复列名称:

CTE不允许重复的列名,因此您必须使用别名来解析它们,最好使用一些命名约定,例如在查询尝试中.

由于某种原因,我在脑海中有一个命名约定,它将为我处理这个场景,但我在文档中找不到它.

您可能想过将DefaultTypeMap.MatchNamesWithUnderscores属性设置为true,但作为属性的代码文档说明:

是否应允许像User_Id这样的列名匹配UserId等属性/字段？

显然这不是解决方案.但是,通过引入自定义命名约定(例如"{prefix}{propertyName}"默认前缀为"{className}_")并通过Dapper实现它,可以轻松解决该问题CustomPropertyTypeMap.这是一个辅助方法,它可以:

public static class CustomNameMap
{
    public static void SetFor<T>(string prefix = null)
    {
        if (prefix == null) prefix = typeof(T).Name + "_";
        var typeMap = new CustomPropertyTypeMap(typeof(T), (type, name) =>
        {
            if (name.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
                name = name.Substring(prefix.Length);
            return type.GetProperty(name);
        });
        SqlMapper.SetTypeMap(typeof(T), typeMap);
    }
}

现在您只需要调用它(一次):

CustomNameMap.SetFor<Location>();

将命名约定应用于您的查询:

WITH TempSites AS(
    SELECT
        [S].[SiteID],
        [S].[Name],
        [S].[Description],
        [L].[LocationID],
        [L].[Name] AS [Location_Name],
        [L].[Description] AS [Location_Description],
        [L].[SiteID] AS [Location_SiteID],
        [L].[ReportingID]
    FROM (
        SELECT * FROM [dbo].[Sites] [1_S]
        WHERE [1_S].[StatusID] = 0
        ORDER BY [1_S].[Name]
        OFFSET 10 * (1 - 1) ROWS
        FETCH NEXT 10 ROWS ONLY
    ) S
        LEFT JOIN [dbo].[Locations] [L] ON [S].[SiteID] = [L].[SiteID]
),
MaxItems AS (SELECT COUNT(SiteID) AS MaxItems FROM Sites)

SELECT *
FROM TempSites, MaxItems

你完成了那部分.当然,如果你愿意,你可以使用更短的前缀,如"Loc_".

将查询结果映射到提供的类:

在这种特殊情况下,您需要使用Query方法重载,该方法允许您传递Func<TFirst, TSecond, TReturn> map委托并将splitOn参数单元化以指定LocationID为拆分列.然而,这还不够.Dapper的多映射功能允许您在需要with 列表(如LINQ )时将单行拆分为多个单个对象(如LINQ ). JoinSiteLocation GroupJoin

它可以通过使用该Query方法投影到临时匿名类型,然后使用常规LINQ生成所需的输出,如下所示:

var sites = cn.Query(sql, (Site site, Location loc) => new { site, loc }, splitOn: "LocationID")
    .GroupBy(e => e.site.SiteID)
    .Select(g =>
    {
        var site = g.First().site;
        site.Locations = g.Select(e => e.loc).Where(loc => loc != null).ToList();
        return site;
    })
    .ToList();

其中cn被打开SqlConnection并且sql是string保持上述查询.

Answer 2

您可以使用ColumnAttributeTypeMapper将列名称与另一个属性映射.

有关详细信息,请参阅我对Gist的第一条评论.

你可以做像这样的映射

public class Site
{
    public int SiteID { get; set; }
    [Column("SiteName")]
    public string Name { get; set; }
    public string Description { get; set; }
    public List<Location> Locations { get; internal set; }
}

public class Location
{
    public int LocationID { get; set; }
    [Column("LocationName")]
    public string Name { get; set; }
    [Column("LocationDescription")]
    public string Description { get; set; }
    public Guid ReportingID { get; set; }
    [Column("LocationSiteID")]
    public int SiteID { get; set; }
}

可以使用以下3种方法之一完成映射

方法1

手动将模型的自定义TypeMapper设置为:

Dapper.SqlMapper.SetTypeMap(typeof(Site), new ColumnAttributeTypeMapper<Site>());
Dapper.SqlMapper.SetTypeMap(typeof(Location), new ColumnAttributeTypeMapper<Location>());

方法2

对于.NET Framework> = v4.0的类库,可以使用PreApplicationStartMethod为自定义类型映射注册类.

using System.Web;
using Dapper;

[assembly: PreApplicationStartMethod(typeof(YourNamespace.Initiator), "RegisterModels")]

namespace YourNamespace
{
    public class Initiator
    {
        private static void RegisterModels()
        {
             SqlMapper.SetTypeMap(typeof(Site), new ColumnAttributeTypeMapper<Site>());
             SqlMapper.SetTypeMap(typeof(Location), new ColumnAttributeTypeMapper<Location>());
             // ...
        }
    }
}

方法3

或者,您可以通过反射和设置类型映射找到应用ColumnAttribute的类.这可能会慢一点,但它会为您自动完成程序集中的所有映射.只需RegisterTypeMaps()在加载程序集后调用即可.

    public static void RegisterTypeMaps()
    {
        var mappedTypes = Assembly.GetAssembly(typeof (Initiator)).GetTypes().Where(
            f =>
            f.GetProperties().Any(
                p =>
                p.GetCustomAttributes(false).Any(
                    a => a.GetType().Name == ColumnAttributeTypeMapper<dynamic>.ColumnAttributeName)));

        var mapper = typeof(ColumnAttributeTypeMapper<>);
        foreach (var mappedType in mappedTypes)
        {
            var genericType = mapper.MakeGenericType(new[] { mappedType });
            SqlMapper.SetTypeMap(mappedType, Activator.CreateInstance(genericType) as SqlMapper.ITypeMap);
        }
    }