摘要：
前言 前言在EFCore中执行Sql语句的方法有：FromSql和ExecuteSqlCommand；在EF6中，SqlQuery与ExecuteSqlCommand不同，而FromSql和SqlQuery非常不同。FromSql的返回值为IQueryable。因此，对于延迟加载，它可以与Linq扩展方法一起使用，但存在许多缺陷。建议在直接执行Sql语句时不要使用FromSql，但EFCore不提供SqlQuery方法。因此，SqlQuery的实现代码将发布在下面供您参考，以便在EFCore中使用。FromSql和ExecuteSqlCommand的使用测试使用SqlServer2008和SqlServerProfiler捕获Sql语句。EFCore版本为1.1.0。
在EFCore中执行Sql语句的方法为：FromSql与ExecuteSqlCommand；在EF6中的为SqlQuery与ExecuteSqlCommand，而FromSql和SqlQuery有很大区别，FromSql返回值为IQueryable，因此为延迟加载的，可以与Linq扩展方法配合使用，但是有不少的坑(EFCore版本为1.1.0)，直接执行Sql语句的建议不要使用FromSql，但是EFCore中并没有提供SqlQuery方法，因此下面会贴出SqlQuery的实现代码供大家参考，以便在EFCore中能使用。
FromSql和ExecuteSqlCommand的使用
测试时使用了SqlServer2008和SqlServer Profiler进行Sql语句捕捉，EFCore的版本为1.1.0。
测试的Entity Model与DbContext
public class MSSqlDBContext : DbContext
{
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder.UseSqlServer(@"data source=localhost;initial catalog=TestDB;Integrated Security=True;");
}
public DbSet<Person> Person { get; set; }
public DbSet<Address> Address { get; set; }
}
[Table(nameof(Person))]
public class Person
{
public int id { get; set; }
public string name { get; set; }
[Column(TypeName = "datetime")]
public DateTime? birthday { get; set; }
public int? addrid { get; set; }
}
[Table(nameof(Address))]
public class Address
{
public int id { get; set; }
public string fullAddress { get; set; }
public double? lat { get; set; }
public double? lon { get; set; }
}
ExecuteSqlCommand
EFCore的ExecuteSqlCommand和EF6的一样，执行非查询的Sql语句：
var db = new MSSqlDBContext();
2 db.Database.ExecuteSqlCommand($"update {nameof(Person)} set name=@name where id=@id", new[]
3 {
4 new SqlParameter("name", "tom1"),
5 new SqlParameter("id", 1),
6 });
FromSql
官方参考文档：https://docs.microsoft.com/en-us/ef/core/querying/raw-sql
简单使用
var db = new MSSqlDBContext();
2 var name = "tom";
3 var list = db.Set<Person>().FromSql($"select * from {nameof(Person)} where {nameof(name)}=@{nameof(name)} ",
4 new SqlParameter(nameof(name), name)).ToList();
生成的Sql：
exec sp_executesql N'select * from Person where name=@name ',N'@name nvarchar(3)',@name=N'tom'
注意：
默认生成的为Person的Model，如果Select获取的字段中不包含Person中的某字段就会抛异常了，例如：下面的语句只获取name字段，并没有包含Person的其他字段，那么抛异常：The required column 'id' was not present in the results of a 'FromSql' operation.
db.Set<Person>().FromSql($"select name from {nameof(Person)} ").ToList();
那么改为：
db.Set<Person>().Select(l => l.name).FromSql($"select name from {nameof(Person)} ").ToList();
执行存储过程
var db = new MSSqlDBContext();
db.Set<Person>().FromSql("exec testproc @id", new SqlParameter("id", 1)).ToList();
生成的Sql：
exec sp_executesql N'exec testproc @id ',N'@id int',@id=1
与Linq扩展方法配合使用
var db = new MSSqlDBContext();
db.Set<Person>().FromSql($"select * from {nameof(Person)} where name=@name ", new SqlParameter("@name", "tom"))
.Select(l => new { l.name, l.birthday }).ToList();
生成的Sql：
exec sp_executesql N'SELECT [l].[name], [l].[birthday]
FROM (
select * from Person where name=@name
) AS [l]',N'@name nvarchar(3)',@name=N'tom'
inner join + order by
var db = new MSSqlDBContext();
(from p in db.Set<Person>().FromSql($"select * from {nameof(Person)} ")
join a in db.Set<Address>().Where(l => true)
on p.addrid equals a.id
select new { p.id, p.name, a.fullAddress }).OrderBy(l => l.id).ToList();
生成的Sql：
SELECT [p].[id], [p].[name], [t].[fullAddress]
FROM (
select * from Person
) AS [p]
INNER JOIN (
SELECT [l0].*
FROM [Address] AS [l0]
) AS [t] ON [p].[addrid] = [t].[id]
ORDER BY [p].[id]
left join + order by
var db = new MSSqlDBContext();
(from p in db.Set<Person>().FromSql($"select * from {nameof(Person)} ")
join a in db.Set<Address>().Where(l => true)
on p.addrid equals a.id into alist
from a in alist.DefaultIfEmpty()
select new { p.id, p.name, fullAddress = a == null ? null : a.fullAddress }).OrderBy(l => l.id).ToList();
生成的Sql：(生成的Sql很有问题，order by后面多了[p].[addrid]，而且生成的select的字段也是多了)
SELECT [p].[id], [p].[addrid], [p].[birthday], [p].[name], [t].[id], [t].[fullAddress], [t].[lat], [t].[lon]
FROM (
select * from Person
) AS [p]
LEFT JOIN (
SELECT [l0].[id], [l0].[fullAddress], [l0].[lat], [l0].[lon]
FROM [Address] AS [l0]
) AS [t] ON [p].[addrid] = [t].[id]
ORDER BY [p].[id], [p].[addrid]
将FromSql换成Where扩展方法试试：
(from p in db.Set<Person>().Where(l => true)
join a in db.Set<Address>().Where(l => true)
on p.addrid equals a.id into alist
from a in alist.DefaultIfEmpty()
select new { p.id, p.name, fullAddress = a == null ? null : a.fullAddress }).OrderBy(l => l.id).ToList();
EFCore生成的Sql（order by后面还是多了[addrid]，select的字段也是多了）：
SELECT [l].[id], [l].[addrid], [l].[birthday], [l].[name], [t].[id], [t].[fullAddress], [t].[lat], [t].[lon]
FROM [Person] AS [l]
LEFT JOIN (
SELECT [l1].[id], [l1].[fullAddress], [l1].[lat], [l1].[lon]
FROM [Address] AS [l1]
) AS [t] ON [l].[addrid] = [t].[id]
ORDER BY [l].[id], [l].[addrid]
而在EF6中生成的Sql，比EFCore的生成好多了：
SELECT
[Project1].[id] AS [id],
[Project1].[name] AS [name],
[Project1].[C1] AS [C1]
FROM ( SELECT
[Extent1].[id] AS [id],
[Extent1].[name] AS [name],
CASE WHEN ([Extent2].[id] IS NULL) THEN CAST(NULL AS varchar(1)) ELSE [Extent2].[fullAddress] END AS [C1]
FROM [dbo].[Person] AS [Extent1]
LEFT OUTER JOIN [dbo].[Address] AS [Extent2] ON [Extent1].[addrid] = [Extent2].[id]
) AS [Project1]
ORDER BY [Project1].[id] ASC
结果说明
FromSql不能代替原来EF6的SqlQuery使用，而且结合Linq扩展方法使用的时候生成的Sql会存在一些问题(EFCore版本为：1.1.0)，那么为了能在EFCore中执行Sql查询语句，下面提供对SqlQuery方法的实现。
SqlQuery的实现
public static IList<T> SqlQuery<T>(DbContext db, string sql, params object[] parameters)
where T : new()
{
//注意：不要对GetDbConnection获取到的conn进行using或者调用Dispose，否则DbContext后续不能再进行使用了，会抛异常
var conn = db.Database.GetDbConnection();
try
{
conn.Open();
using (var command = conn.CreateCommand())
{
command.CommandText = sql;
command.Parameters.AddRange(parameters);
var propts = typeof(T).GetProperties();
var rtnList = new List<T>();
T model;
object val;
using (var reader = command.ExecuteReader())
{
while (reader.Read())
{
model = new T();
foreach (var l in propts)
{
val = reader[l.Name];
if (val == DBNull.Value)
{
l.SetValue(model, null);
}
else
{
l.SetValue(model, val);
}
}
rtnList.Add(model);
}
}
return rtnList;
}
}
finally
{
conn.Close();
}
}
使用：
var db = new MSSqlDBContext();
string name = "tom";
var list = SqlQuery<PAModel>(db,
$" select p.id, p.name, a.fullAddress, a.lat, a.lon " +
$" from ( select * from {nameof(Person)} where {nameof(name)}=@{nameof(name)} ) as p " +
$" left join {nameof(Address)} as a on p.addrid = a.id ",
new[] { new SqlParameter(nameof(name), name) });
生成的Sql：
exec sp_executesql N' select p.id, p.name, a.fullAddress, a.lat, a.lon from ( select * from Person where name=@name ) as p left join Address as a on p.addrid = a.id ',N'@name nvarchar(3)',@name=N'tom'