Intro
To improve performance, I sometimes use Raw SQL Queries.
In ASP.NET Framework(Entity Framework 6), I can do this.
using (var context = new BloggingContext())
{
context.Database.ExecuteSqlCommand(
"UPDATE dbo.Blogs SET Name = 'Another Name' WHERE BlogId = 1");
}
But in ASP.NET Core, I can't use "ExecuteSqlCommand".
So in this time, I try it.
Environments
- .NET ver.5.0.100-rc.1.20452.10
- Microsoft.EntityFrameworkCore ver.5.0.0-rc.1.20451.13
- Npgsql.EntityFrameworkCore.PostgreSQL ver.5.0.0-rc1
- NLog.Web.AspNetCore ver.4.9.3
Execute Raw SQL Queries
I only can execute Raw SQL Queries through "DbSet".
...
var blogs = context.Blogs
.FromSqlRaw("EXECUTE dbo.GetMostPopularBlogsForUser {0}", user)
.ToList();
But how about projection class?
For example, I want to get data by this SQL query.
SELECT c."Id", c."Name" AS "CompanyName", b."Id" AS "BookId", b."Name" AS "BookName",
b."PublishDate", b."GenreId", b."Price" FROM "Companies" c
INNER JOIN LATERAL(SELECT * FROM "Books" innerb
WHERE innerb."CompanyId" = c."Id" ORDER BY innerb."Id" DESC LIMIT 1) b
ON c."Id" = b."CompanyId"
And I want to set into this class.
SearchedCompany.cs
using System;
using System.ComponentModel.DataAnnotations;
namespace BookStoreSample.Books
{
public class SearchedCompany
{
[Key]
public int CompanyId { get; set; }
public string CompanyName { get; set; } = "";
public int BookId { get; set; }
public string BookName { get; set; } = "";
public DateTime? PublishDate { get; set; }
public int GenreId { get; set; }
public decimal? Price { get; set; }
}
}
I thought classes in "DbSet<T>" should match a table in the database.
But I can also use projection classes like "SearchedCompany".
BookStoreContext.cs
using BookStoreSample.Books;
using Microsoft.EntityFrameworkCore;
namespace BookStoreSample.Models
{
public class BookStoreContext: DbContext
{
...
public DbSet<SearchedCompany> SearchedCompanies => Set<SearchedCompany>();
}
}
So I can execute SQL query like below.
BookSearchSample.cs
...
public async Task<List<SearchedCompany>> SearchCompaniesAsync()
{
var sql = "SELECT c.\"Id\", c.\"Name\" AS \"CompanyName\", " +
"b.\"Id\" AS \"BookId\", b.\"Name\" AS \"BookName\", " +
"b.\"PublishDate\", b.\"GenreId\", b.\"Price\" FROM \"Companies\" c " +
"INNER JOIN LATERAL(SELECT * FROM \"Books\" innerb " +
"WHERE innerb.\"CompanyId\" = c.\"Id\" ORDER BY innerb.\"Id\" DESC LIMIT 1) b " +
"ON c.\"Id\" = b.\"CompanyId\" ";
return await _context.SearchedCompanies.FromSqlRaw(sql)
.ToListAsync();
}
...
One important thing is the class must have "[Key]" or a property what is named "Id".
Skip Raw SQL Queries?
If I remove "FromSqlRaw" from the sample, can I get empty result?
...
public async Task<List<SearchedCompany>> SearchCompaniesAsync()
{
// Don't do this
return await _context.SearchedCompanies
.ToListAsync();
}
...
The answer is getting an exception.
2020-10-10 07:04:17.1997|13|ERROR|Microsoft.AspNetCore.Server.Kestrel|Connection id "0HM3CJT1I07AV", Request id "0HM3CJT1I07AV:00000002": An unhandled exception was thrown by the application. Npgsql.PostgresException (0x80004005): 42P01: relation "SearchedCompanies" does not exist
at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<<DoReadMessage>g__ReadMessageLong|0>d.MoveNext()
...
Except their names, I still don't know how can I distinguish them.
// OK
var companies = await _context.Companies
.ToListAsync();
// Exception
var searchedCompanies = await _context.SearchedCompanies
.ToListAsync();
Where clauses
Of cource I can add where clauses into "sql" as string.
But it can cause SQL injection.
Because "FromSqlRaw" also can use Linq, so if the where clauses aren't very complecated, I think I shall use Linq to add them.
BookSearchSample.cs
...
public async Task<List<SearchedCompany>> SearchCompaniesAsync()
{
var sql = "SELECT c.\"Id\", c.\"Name\" AS \"CompanyName\", " +
"b.\"Id\" AS \"BookId\", b.\"Name\" AS \"BookName\", " +
"b.\"PublishDate\", b.\"GenreId\", b.\"Price\" FROM \"Companies\" c " +
"INNER JOIN LATERAL(SELECT * FROM \"Books\" innerb " +
"WHERE innerb.\"CompanyId\" = c.\"Id\" ORDER BY innerb.\"Id\" DESC LIMIT 1) b " +
"ON c.\"Id\" = b.\"CompanyId\" ";
return await _context.SearchedCompanies.FromSqlRaw(sql)
.Where(c => c.CompanyId == 1)
.ToListAsync();
}
...
According to logs, ".Where(c => c.CompanyId == 1)" was also converted into SQL queries.
Generated SQL queries
SELECT s."Id", s."BookId", s."BookName", s."CompanyName", s."GenreId", s."Price", s."PublishDate"
FROM (
SELECT c."Id", c."Name" AS "CompanyName", b."Id" AS "BookId", b."Name" AS "BookName", b."PublishDate", b."GenreId", b."Price" FROM "Companies" c INNER JOIN LATERAL(SELECT * FROM "Books" innerb WHERE innerb."CompanyId" = c."Id" ORDER BY innerb."Id" DESC LIMIT 1) b ON c."Id" = b."CompanyId"
) AS s
WHERE s."Id" = 1
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