Cursor pagination (#3)

* Cursor pagination

* Create the separate file with the PageInfo type.

Author: debugger84

examples/cursor/README.md

@@ -0,0 +1,119 @@
+# Pagination queries generation example
+
+This is an example based on the "simple" example. It shows how to generate pagination queries using the sqlc tool.
+
+Main differences from the "simple" example:
+1. The `storage/query.sql` file contains the `ListAuthors` query without the `limit` and `offset` parameters.
+But it has the `-- paginated: offset` comment. It means that the `ListAuthors` query will be paginated by the `offset` parameter.
+In the future it will be possible to paginate queries by cursor. In this case the `-- paginated: cursor` comment should be used.
+```sql
+-- name: ListAuthors :many
+-- gql: Query
+-- paginated: offset
+SELECT * FROM authors
+ORDER BY name;
+```
+2. The `storage/sqlc.yaml` uses the https://github.com/debugger84/sqlc-gen-go plugin to generate the pagination queries instead of the original one.
+3. After running the generation the generated code contains the `ListAuthors` query with the `offset` and `limit` parameters. And the `AuthorPage` type returned from the query instead of `[]Author`.
+```graphql
+type AuthorPage @goModel(model: "cursor/storage.AuthorPage") {
+    items: [Author!]!
+    total: Int!
+    hasNext: Boolean!
+}
+
+input ListAuthorsInput @goModel(model: "cursor/storage.ListAuthorsParams") {
+    limit: Int!
+    offset: Int!
+}
+
+extend type Query {
+    listAuthors(request: ListAuthorsInput!): AuthorPage!
+}
+```
+## How to use
+1. Install sqlc (https://docs.sqlc.dev/en/latest/overview/install.html)
+2. Add new queries to the storage/query.sql file
+3. Mark all new queries with the comment: 
+```sql
+-- gql: <extended_type>.<query_name>
+-- paginated: offset
+``` 
+For example:
+```sql
+-- gql: Query.getAllAuthors
+-- paginated: offset
+SELECT * FROM authors;
+```
+
+3. Run the following commands to generate golang and graphql code:
+```bash
+cd examples/cursor 
+sqlc generate -f storage/sqlc.yaml
+```
+4. The generated code will be in the storage and graphql folders
+5. Run the following command to generate the GraphQL resolvers by GraphQl schema:
+```bash
+go run github.com/99designs/gqlgen generate
+```
+It will generate the resolvers in the graph/resolver folder.
+
+6. Find the changes in the graph/resolver folder. 
+The changes will consist of the new queries with panics like this.
+```go
+func (r *queryResolver) GetAllAuthors(ctx context.Context, request storage.GetAllAuthorsParams) (storage.AuthorPage, error) {
+    panic(fmt.Errorf("not implemented"))
+}
+```
+
+7. Change the panic to the real implementation of the query. For example:
+```go
+func (r *queryResolver) GetAllAuthors(ctx context.Context, request storage.GetAllAuthorsParams) (storage.AuthorPage, error) {
+    return r.Queries.GetAllAuthors(ctx, request)
+}
+```
+
+8. Apply migrations to the database:
+```bash
+docker run --rm -it --network=host -v "$(pwd)/storage:/db" ghcr.io/amacneil/dbmate -u "postgres://postgres:foobar@localhost:5432/test?sslmode=disable" up
+```
+
+9. Run the following command to start the server:
+```bash
+PORT=8081 PG_URI="postgres://postgres:foobar@127.0.0.1:5432/test?sslmode=disable" go run server.go
+```
+
+10. Open the browser and go to the http://localhost:8081/. You will see the GraphQL playground.
+11. Try to add several authors to the database:
+```graphql
+mutation {
+    createAuthor(request:{name:"John Doe", bio:"Unknown guy"}) {
+        id
+        name
+    }
+}
+```
+12. Try to get all authors:
+```graphql
+{
+    listAuthors(request:{limit:10, offset:0}){total, hasNext, items{id, name}}
+}
+
+```
+and you will see the list of authors like this:
+```json
+{
+  "data": {
+    "listAuthors": {
+      "total": 1,
+      "hasNext": false,
+      "items": [
+        {
+          "id": 1,
+          "name": "John Doe"
+        }
+      ]
+    }
+  }
+}
+```

examples/cursor/go.mod

@@ -0,0 +1,32 @@
+module cursor
+
+go 1.22.2
+
+require (
+	github.com/99designs/gqlgen v0.17.49
+	github.com/jackc/pgx/v5 v5.6.0
+	github.com/vektah/gqlparser/v2 v2.5.16
+)
+
+require (
+	github.com/agnivade/levenshtein v1.1.1 // indirect
+	github.com/cpuguy83/go-md2man/v2 v2.0.4 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/gorilla/websocket v1.5.0 // indirect
+	github.com/hashicorp/golang-lru/v2 v2.0.7 // indirect
+	github.com/jackc/pgpassfile v1.0.0 // indirect
+	github.com/jackc/pgservicefile v0.0.0-20221227161230-091c0ba34f0a // indirect
+	github.com/kr/text v0.1.0 // indirect
+	github.com/mitchellh/mapstructure v1.5.0 // indirect
+	github.com/rogpeppe/go-internal v1.12.0 // indirect
+	github.com/russross/blackfriday/v2 v2.1.0 // indirect
+	github.com/sosodev/duration v1.3.1 // indirect
+	github.com/urfave/cli/v2 v2.27.2 // indirect
+	github.com/xrash/smetrics v0.0.0-20240312152122-5f08fbb34913 // indirect
+	golang.org/x/crypto v0.20.0 // indirect
+	golang.org/x/mod v0.18.0 // indirect
+	golang.org/x/sync v0.7.0 // indirect
+	golang.org/x/text v0.16.0 // indirect
+	golang.org/x/tools v0.22.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

examples/cursor/go.sum

@@ -0,0 +1,81 @@
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examples/cursor/gqlgen.yml

@@ -0,0 +1,87 @@
+# Where are all the schema files located? globs are supported eg  src/**/*.graphqls
+schema:
+  - graphql/*.graphql
+
+# Where should the generated server code go?
+exec:
+  filename: graph/gen/generated.go
+  package: gen
+
+# Uncomment to enable federation
+# federation:
+#   filename: graph/federation.go
+#   package: graph
+
+# Where should any generated models go?
+model:
+  filename: graph/model/models_gen.go
+  package: model
+
+# Where should the resolver implementations go?
+resolver:
+  layout: follow-schema
+  dir: graph/resolver
+  package: resolver
+  filename_template: "{name}.resolvers.go"
+  # Optional: turn on to not generate template comments above resolvers
+  # omit_template_comment: false
+
+# Optional: turn on use ` + "`" + `gqlgen:"fieldName"` + "`" + ` tags in your models
+# struct_tag: json
+
+# Optional: turn on to use []Thing instead of []*Thing
+omit_slice_element_pointers: true
+
+# Optional: turn on to omit Is<Name>() methods to interface and unions
+# omit_interface_checks : true
+
+# Optional: turn on to skip generation of ComplexityRoot struct content and Complexity function
+# omit_complexity: false
+
+# Optional: turn on to not generate any file notice comments in generated files
+# omit_gqlgen_file_notice: false
+
+# Optional: turn on to exclude the gqlgen version in the generated file notice. No effect if `omit_gqlgen_file_notice` is true.
+# omit_gqlgen_version_in_file_notice: false
+
+# Optional: turn off to make struct-type struct fields not use pointers
+# e.g. type Thing struct { FieldA OtherThing } instead of { FieldA *OtherThing }
+# struct_fields_always_pointers: true
+
+# Optional: turn off to make resolvers return values instead of pointers for structs
+resolvers_always_return_pointers: false
+
+# Optional: turn on to return pointers instead of values in unmarshalInput
+# return_pointers_in_unmarshalinput: false
+
+# Optional: wrap nullable input fields with Omittable
+# nullable_input_omittable: true
+
+# Optional: set to speed up generation time by not performing a final validation pass.
+# skip_validation: true
+
+# Optional: set to skip running `go mod tidy` when generating server code
+# skip_mod_tidy: true
+
+# gqlgen will search for any type names in the schema in these go packages
+# if they match it will use them, otherwise it will generate them.
+autobind:
+#  - "cursor/graph/model"
+
+# This section declares type mapping between the GraphQL and go type systems
+#
+# The first line in each type will be used as defaults for resolver arguments and
+# modelgen, the others will be allowed when binding to fields. Configure them to
+# your liking
+models:
+  ID:
+    model:
+      - github.com/99designs/gqlgen/graphql.ID
+      - github.com/99designs/gqlgen/graphql.Int
+      - github.com/99designs/gqlgen/graphql.Int64
+      - github.com/99designs/gqlgen/graphql.Int32
+  Int:
+    model:
+      - github.com/99designs/gqlgen/graphql.Int
+      - github.com/99designs/gqlgen/graphql.Int64
+      - github.com/99designs/gqlgen/graphql.Int32