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Updated example to match with current implementation #1208

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Nov 3, 2022
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Updated example to match with current implementation #1208

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168 changes: 114 additions & 54 deletions docs/internals/queries.md
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Original file line number Diff line number Diff line change
Expand Up @@ -22,66 +22,76 @@ Processing a request involves the following steps:
- `JsonApiResourceService` contains no more usage of `IQueryable`.
- `EntityFrameworkCoreRepository` delegates to `QueryableBuilder` to transform the `QueryLayer` tree into `IQueryable` expression trees.
`QueryBuilder` depends on `QueryClauseBuilder` implementations that visit the tree nodes, transforming them to `System.Linq.Expression` equivalents.
The `IQueryable` expression trees are executed by Entity Framework Core, which produces SQL statements out of them.
The `IQueryable` expression trees are passed to Entity Framework Core, which produces SQL statements out of them.
- `JsonApiWriter` transforms resource objects into json response.

# Example
To get a sense of what this all looks like, let's look at an example query string:

```
/api/v1/blogs?
include=owner,articles.revisions.author&
filter=has(articles)&
sort=count(articles)&
include=owner,posts.comments.author&
filter=has(posts)&
sort=count(posts)&
page[number]=3&
fields[blogs]=title&
filter[articles]=and(not(equals(author.firstName,null)),has(revisions))&
sort[articles]=author.lastName&
fields[articles]=url&
filter[articles.revisions]=and(greaterThan(publishTime,'2001-01-01'),startsWith(author.firstName,'J'))&
sort[articles.revisions]=-publishTime,author.lastName&
fields[revisions]=publishTime
filter[posts]=and(not(equals(author.userName,null)),has(comments))&
sort[posts]=author.displayName&
fields[blogPosts]=url&
filter[posts.comments]=and(greaterThan(createdAt,'2001-01-01Z'),startsWith(author.userName,'J'))&
sort[posts.comments]=-createdAt,author.displayName&
fields[comments]=createdAt
```

After parsing, the set of scoped expressions is transformed into the following tree by `QueryLayerComposer`:

```
QueryLayer<Blog>
{
Include: owner,articles.revisions
Filter: has(articles)
Sort: count(articles)
Include: owner,posts.comments.author
Filter: has(posts)
Sort: count(posts)
Pagination: Page number: 3, size: 5
Projection
Selection
{
title
id
owner: QueryLayer<Author>
FieldSelectors<Blog>
{
Sort: id
Pagination: Page number: 1, size: 5
}
articles: QueryLayer<Article>
{
Filter: and(not(equals(author.firstName,null)),has(revisions))
Sort: author.lastName
Pagination: Page number: 1, size: 5
Projection
title
id
posts: QueryLayer<BlogPost>
{
url
id
revisions: QueryLayer<Revision>
Filter: and(not(equals(author.userName,null)),has(comments))
Sort: author.displayName
Pagination: Page number: 1, size: 5
Selection
{
Filter: and(greaterThan(publishTime,'2001-01-01'),startsWith(author.firstName,'J'))
Sort: -publishTime,author.lastName
Pagination: Page number: 1, size: 5
Projection
FieldSelectors<BlogPost>
{
publishTime
url
id
comments: QueryLayer<Comment>
{
Filter: and(greaterThan(createdAt,'2001-01-01'),startsWith(author.userName,'J'))
Sort: -createdAt,author.displayName
Pagination: Page number: 1, size: 5
Selection
{
FieldSelectors<Comment>
{
createdAt
id
author: QueryLayer<WebAccount>
{
}
}
}
}
}
}
}
owner: QueryLayer<WebAccount>
{
}
}
}
}
Expand All @@ -90,36 +100,86 @@ QueryLayer<Blog>
Next, the repository translates this into a LINQ query that the following C# code would represent:

```c#
var query = dbContext.Blogs
IQueryable<Blog> query = dbContext.Blogs
.Include("Posts.Comments.Author")
.Include("Owner")
.Include("Articles.Revisions")
.Where(blog => blog.Articles.Any())
.OrderBy(blog => blog.Articles.Count)
.Where(blog => blog.Posts.Any())
.OrderBy(blog => blog.Posts.Count)
.Skip(10)
.Take(5)
.Select(blog => new Blog
{
Title = blog.Title,
Id = blog.Id,
Owner = blog.Owner,
Articles = new List<Article>(blog.Articles
.Where(article => article.Author.FirstName != null && article.Revisions.Any())
.OrderBy(article => article.Author.LastName)
Posts = blog.Posts
.Where(blogPost => blogPost.Author.UserName != null && blogPost.Comments.Any())
.OrderBy(blogPost => blogPost.Author.DisplayName)
.Take(5)
.Select(article => new Article
.Select(blogPost => new BlogPost
{
Url = article.Url,
Id = article.Id,
Revisions = new HashSet<Revision>(article.Revisions
.Where(revision => revision.PublishTime > DateTime.Parse("2001-01-01") && revision.Author.FirstName.StartsWith("J"))
.OrderByDescending(revision => revision.PublishTime)
.ThenBy(revision => revision.Author.LastName)
Url = blogPost.Url,
Id = blogPost.Id,
Comments = blogPost.Comments
.Where(comment => comment.CreatedAt > DateTime.Parse("2001-01-01Z") &&
comment.Author.UserName.StartsWith("J"))
.OrderByDescending(comment => comment.CreatedAt)
.ThenBy(comment => comment.Author.DisplayName)
.Take(5)
.Select(revision => new Revision
.Select(comment => new Comment
{
PublishTime = revision.PublishTime,
Id = revision.Id
}))
}))
CreatedAt = comment.CreatedAt,
Id = comment.Id,
Author = comment.Author
}).ToHashSet()
}).ToList(),
Owner = blog.Owner
});
```

The LINQ query gets translated by Entity Framework Core into the following SQL:

```sql
SELECT t."Title", t."Id", a."Id", t2."Url", t2."Id", t2."Id0", t2."CreatedAt", t2."Id1", t2."Id00", t2."DateOfBirth", t2."DisplayName", t2."EmailAddress", t2."Password", t2."PersonId", t2."PreferencesId", t2."UserName", a."DateOfBirth", a."DisplayName", a."EmailAddress", a."Password", a."PersonId", a."PreferencesId", a."UserName"
FROM (
SELECT b."Id", b."OwnerId", b."Title", (
SELECT COUNT(*)::INT
FROM "Posts" AS p0
WHERE b."Id" = p0."ParentId") AS c
FROM "Blogs" AS b
WHERE EXISTS (
SELECT 1
FROM "Posts" AS p
WHERE b."Id" = p."ParentId")
ORDER BY (
SELECT COUNT(*)::INT
FROM "Posts" AS p0
WHERE b."Id" = p0."ParentId")
LIMIT @__Create_Item1_1 OFFSET @__Create_Item1_0
) AS t
LEFT JOIN "Accounts" AS a ON t."OwnerId" = a."Id"
LEFT JOIN LATERAL (
SELECT t0."Url", t0."Id", t0."Id0", t1."CreatedAt", t1."Id" AS "Id1", t1."Id0" AS "Id00", t1."DateOfBirth", t1."DisplayName", t1."EmailAddress", t1."Password", t1."PersonId", t1."PreferencesId", t1."UserName", t0."DisplayName" AS "DisplayName0", t1."ParentId"
FROM (
SELECT p1."Url", p1."Id", a0."Id" AS "Id0", a0."DisplayName"
FROM "Posts" AS p1
LEFT JOIN "Accounts" AS a0 ON p1."AuthorId" = a0."Id"
WHERE (t."Id" = p1."ParentId") AND (((a0."UserName" IS NOT NULL)) AND EXISTS (
SELECT 1
FROM "Comments" AS c
WHERE p1."Id" = c."ParentId"))
ORDER BY a0."DisplayName"
LIMIT @__Create_Item1_1
) AS t0
LEFT JOIN (
SELECT t3."CreatedAt", t3."Id", t3."Id0", t3."DateOfBirth", t3."DisplayName", t3."EmailAddress", t3."Password", t3."PersonId", t3."PreferencesId", t3."UserName", t3."ParentId"
FROM (
SELECT c0."CreatedAt", c0."Id", a1."Id" AS "Id0", a1."DateOfBirth", a1."DisplayName", a1."EmailAddress", a1."Password", a1."PersonId", a1."PreferencesId", a1."UserName", c0."ParentId", ROW_NUMBER() OVER(PARTITION BY c0."ParentId" ORDER BY c0."CreatedAt" DESC, a1."DisplayName") AS row
FROM "Comments" AS c0
LEFT JOIN "Accounts" AS a1 ON c0."AuthorId" = a1."Id"
WHERE (c0."CreatedAt" > @__Create_Item1_2) AND ((@__Create_Item1_3 = '') OR (((a1."UserName" IS NOT NULL)) AND ((a1."UserName" LIKE @__Create_Item1_3 || '%' ESCAPE '') AND (left(a1."UserName", length(@__Create_Item1_3))::text = @__Create_Item1_3::text))))
) AS t3
WHERE t3.row <= @__Create_Item1_1
) AS t1 ON t0."Id" = t1."ParentId"
) AS t2 ON TRUE
ORDER BY t.c, t."Id", a."Id", t2."DisplayName0", t2."Id", t2."Id0", t2."ParentId", t2."CreatedAt" DESC, t2."DisplayName", t2."Id1"
```