EF Core 最终选择投影在使用 UNION

如何解决EF Core 最终选择投影在使用 UNION

我有 5 张桌子：

• 学生
• 学生所在地
• 位置
• 地区
• 区域详情

在下面的代码中，当我的 IQueryable 没有 UNION 时，选择投影有助于生成具有所需列的 SQL，并忽略所有其他不必要的列。但是当我包含 UNION 时，看起来选择投影没有帮助。生成的 SQL 包含查询中所有实体的所有列。

就像第一个查询

locationStudentsQuery
    .Select(x => new StudentForDynamicQuery { StudentId = x.StudentId })
    .ToList()

如何使用 UNION 进行第二次查询

locationStudentsQuery.Union(regionStudentsQuery)
    .Select(x => new StudentForDynamicQuery { StudentId = x.StudentId })
    .ToList()

只生成需要的列的 SQL？

public class StudentForDynamicQuery { public long StudentId { get; set; } }

var locationStudentsQuery = context.Set<StudentEntity>().AsNoTracking()
    .Join(context.Set<StudentLocationEntity>().AsNoTracking(),outer => outer.StudentId,inner => inner.StudentId,(outer,inner) => new { outer.StudentId,inner.LocationId })
    .Join(context.Set<LocationEntity>().AsNoTracking(),outer => outer.LocationId,inner => inner.LocationId,(outer2,inner2) => new { outer2.StudentId });

var result = locationStudentsQuery.Select(x => new StudentForDynamicQuery { StudentId = x.StudentId }).ToList();

SELECT r.student_id
FROM student AS r
INNER JOIN 
    (SELECT r0.location_id,r0.student_id
        FROM student_location AS r0) AS t ON r.student_id = t.student_id
INNER JOIN 
    (SELECT l.location_id
        FROM location AS l) AS t0 ON t.location_id = t0.location_id;

var locationStudentsQuery = context.Set<StudentEntity>().AsNoTracking()
    .Join(context.Set<StudentLocationEntity>().AsNoTracking(),inner2) => new { outer2.StudentId });

    var regionStudentsQuery = query
    .Join(context.Set<StudentLocationEntity>().AsNoTracking(),inner.RegionId })
    .Join(context.Set<RegionDetailEntity>().AsNoTracking(),outer => outer.RegionId,inner => inner.RegionId,inner2) => new { outer2.StudentId,inner2.LocationId })
    .Join(context.Set<LocationEntity>().AsNoTracking(),(outer3,inner3) => new { outer3.StudentId });
var result = locationStudentsQuery.Union(regionStudentsQuery).Select(x => new StudentForDynamicQuery { StudentId = x.StudentId }).ToList();

SELECT r.student_id AS "StudentId"
FROM student AS r
INNER JOIN (
    SELECT 

    r0.student_location_id,r0.create_by,r0.create_date_time,r0.last_change_by,r0.last_change_date_time,r0.location_id,r0.student_id,r0.region_id

    FROM student_location AS r0
) AS t ON r.student_id = t.student_id
INNER JOIN (
    SELECT 

    l.location_id,l.city,l.country_code,l.create_by,l.create_date_time,l.last_change_by,l.last_change_date_time,l.postal_code,l.state_code

    FROM location AS l
) AS t0 ON t.location_id = t0.location_id
UNION
SELECT r1.student_id AS "StudentId"
FROM student AS r1
INNER JOIN (
    SELECT 

    r2.student_location_id,r2.create_by,r2.create_date_time,r2.last_change_by,r2.last_change_date_time,r2.location_id,r2.student_id,r2.region_id

    FROM student_location AS r2
) AS t1 ON r1.student_id = t1.student_id
INNER JOIN (
    SELECT 

    r3.region_detail_id,r3.create_by,r3.create_date_time,r3.last_change_by,r3.last_change_date_time,r3.location_id,r3.region_id

    FROM region_detail AS r3
) AS t2 ON t1.region_id = t2.region_id
INNER JOIN (
    SELECT 

    l0.location_id,l0.city,l0.country_code,l0.create_by,l0.create_date_time,l0.last_change_by,l0.last_change_date_time,l0.postal_code,l0.state_code

    FROM location AS l0
) AS t3 ON t2.location_id = t3.location_id