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前言

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();
            db.Database.ExecuteSqlCommand($"update {nameof(Person)} set name=@name where id=@id", new[] 
            {
                new SqlParameter("name", "tom1"),
                new SqlParameter("id", 1),
            });

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();
            var name = "tom";
            var list = db.Set<Person>().FromSql($"select * from {nameof(Person)} where {nameof(name)}=@{nameof(name)} ", 
                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'