https://github.com/pilagod/gorm-cursor-paginator
A paginator doing cursor-based pagination based on GORM
https://github.com/pilagod/gorm-cursor-paginator
cursor-pagination go golang gorm pagination
Last synced: about 1 month ago
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A paginator doing cursor-based pagination based on GORM
- Host: GitHub
- URL: https://github.com/pilagod/gorm-cursor-paginator
- Owner: pilagod
- License: mit
- Created: 2018-10-09T10:09:20.000Z (over 6 years ago)
- Default Branch: master
- Last Pushed: 2024-10-16T06:08:36.000Z (8 months ago)
- Last Synced: 2025-04-03T06:08:15.406Z (2 months ago)
- Topics: cursor-pagination, go, golang, gorm, pagination
- Language: Go
- Homepage: https://github.com/pilagod/gorm-cursor-paginator
- Size: 220 KB
- Stars: 199
- Watchers: 5
- Forks: 44
- Open Issues: 4
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# gorm-cursor-paginator  [](https://coveralls.io/github/pilagod/gorm-cursor-paginator?branch=master) [](https://goreportcard.com/report/github.com/pilagod/gorm-cursor-paginator)
A paginator doing cursor-based pagination based on [GORM](https://github.com/go-gorm/gorm)
> This doc is for v2, which uses [GORM v2](https://github.com/go-gorm/gorm). If you are using [GORM v1](https://github.com/jinzhu/gorm), please checkout [v1 doc](https://github.com/pilagod/gorm-cursor-paginator/tree/v1).
## Features
- Query extendable.
- Multiple paging keys.
- Pagination across custom types (e.g. JSON)
- Paging rule customization for each key.
- GORM `column` tag supported.
- Error handling enhancement.
- Exporting `cursor` module for advanced usage.
- Implement custom codec for cursor encoding/decoding.
## Installation
```sh
go get -u github.com/pilagod/gorm-cursor-paginator/v2
```
## Usage By Example
```go
import (
"github.com/pilagod/gorm-cursor-paginator/v2/paginator"
)
```
Given an `User` model for example:
```go
type User struct {
ID int
JoinedAt time.Time `gorm:"column:created_at"`
}
```
We first need to create a `paginator.Paginator` for `User`, here are some useful patterns:
1. Configure by `paginator.Option`, those functions with `With` prefix are factories for `paginator.Option`:
```go
func CreateUserPaginator(
cursor paginator.Cursor,
order *paginator.Order,
limit *int,
) *paginator.Paginator {
opts := []paginator.Option{
&paginator.Config{
Keys: []string{"ID", "JoinedAt"},
Limit: 10,
Order: paginator.ASC,
},
}
if limit != nil {
opts = append(opts, paginator.WithLimit(*limit))
}
if order != nil {
opts = append(opts, paginator.WithOrder(*order))
}
if cursor.After != nil {
opts = append(opts, paginator.WithAfter(*cursor.After))
}
if cursor.Before != nil {
opts = append(opts, paginator.WithBefore(*cursor.Before))
}
return paginator.New(opts...)
}
```
2. Configure by setters on `paginator.Paginator`:
```go
func CreateUserPaginator(
cursor paginator.Cursor,
order *paginator.Order,
limit *int,
) *paginator.Paginator {
p := paginator.New(
&paginator.Config{
Keys: []string{"ID", "JoinedAt"},
Limit: 10,
Order: paginator.ASC,
},
)
if order != nil {
p.SetOrder(*order)
}
if limit != nil {
p.SetLimit(*limit)
}
if cursor.After != nil {
p.SetAfterCursor(*cursor.After)
}
if cursor.Before != nil {
p.SetBeforeCursor(*cursor.Before)
}
return p
}
```
3. Configure by `paginator.Rule` for fine grained setting for each key:
> Please refer to [Specification](#specification) for details of `paginator.Rule`.
```go
func CreateUserPaginator(/* ... */) {
p := paginator.New(
&paginator.Config{
Rules: []paginator.Rule{
{
Key: "ID",
},
{
Key: "JoinedAt",
Order: paginator.DESC,
SQLRepr: "users.created_at",
NULLReplacement: "1970-01-01",
},
},
Limit: 10,
// Order here will apply to keys without order specified.
// In this example paginator will order by "ID" ASC, "JoinedAt" DESC.
Order: paginator.ASC,
},
)
// ...
return p
}
```
4. By default the library encodes cursors with `base64`. If a custom encoding/decoding implementation is required, this can be implemented and passed as part of the configuration:
First implement your custom codec such that it conforms to the `CursorCodec` interface:
```go
type CursorCodec interface {
// Encode encodes model fields into cursor
Encode(
fields []pc.EncoderField,
model interface{},
) (string, error)
// Decode decodes cursor into model fields
Decode(
fields []pc.DecoderField,
cursor string,
model interface{},
) ([]interface{}, error)
}
type customCodec struct {}
func (cc *CustomCodec) Encode(fields []pc.EncoderField, model interface{}) (string, error) {
...
}
func (cc *CustomCodec) Decode(fields []pc.DecoderField, cursor string, model interface{}) ([]interface{}, error) {
...
}
```
Then pass an instance of your codec during initialisation:
```go
func CreateUserPaginator(/* ... */) {
codec := &customCodec{}
p := paginator.New(
&paginator.Config{
Rules: []paginator.Rule{
{
Key: "ID",
},
{
Key: "JoinedAt",
Order: paginator.DESC,
SQLRepr: "users.created_at",
NULLReplacement: "1970-01-01",
},
},
Limit: 10,
// supply a custom implementation for the encoder/decoder
CursorCodec: codec,
// Order here will apply to keys without order specified.
// In this example paginator will order by "ID" ASC, "JoinedAt" DESC.
Order: paginator.ASC,
},
)
// ...
return p
}
```
After knowing how to setup the paginator, we can start paginating `User` with GORM:
```go
func FindUsers(db *gorm.DB, query Query) ([]User, paginator.Cursor, error) {
var users []User
// extend query before paginating
stmt := db.
Select(/* fields */).
Joins(/* joins */).
Where(/* queries */)
// create paginator for User model
p := CreateUserPaginator(/* config */)
// find users with pagination
result, cursor, err := p.Paginate(stmt, &users)
// this is paginator error, e.g., invalid cursor
if err != nil {
return nil, paginator.Cursor{}, err
}
// this is gorm error
if result.Error != nil {
return nil, paginator.Cursor{}, result.Error
}
return users, cursor, nil
}
```
The second value returned from `paginator.Paginator.Paginate` is a `paginator.Cursor` struct, which is same as `cursor.Cursor` struct:
```go
type Cursor struct {
After *string `json:"after" query:"after"`
Before *string `json:"before" query:"before"`
}
```
That's all! Enjoy paginating in the GORM world. :tada:
> For more paginating examples, please checkout [example/main.go](https://github.com/pilagod/gorm-cursor-paginator/blob/master/example/main.go) and [paginator/paginator_paginate_test.go](https://github.com/pilagod/gorm-cursor-paginator/blob/master/paginator/paginator_paginate_test.go)
>
> For manually encoding/decoding cursor exmaples, please check out [cursor/encoding_test.go](https://github.com/pilagod/gorm-cursor-paginator/blob/master/cursor/encoding_test.go)
## Specification
### paginator.Paginator
Default options used by paginator when not specified:
- `Keys`: `[]string{"ID"}`
- `Limit`: `10`
- `Order`: `paginator.DESC`
- `AllowTupleCmp`: `paginator.FALSE`
When cursor uses more than one key/rule, paginator instances by default generate SQL that is compatible with almost all database management systems. But this query can be very inefficient and can result in a lot of database scans even when proper indices are in place. By enabling the `AllowTupleCmp` option, paginator will emit a slightly different SQL query when all cursor keys are ordered in the same way.
For example, let us assume we have the following code:
```go
paginator.New(
paginator.WithKeys([]string{"CreatedAt", "ID"}),
paginator.WithAfter(after),
paginator.WithLimit(3),
).Paginate(db, &result)
```
The query that hits our database in this case would look something like this:
```sql
SELECT *
FROM orders
WHERE orders.created_at > $1
OR orders.created_at = $2 AND orders.id > $3
ORDER BY orders.created_at ASC, orders.id ASC
LIMIT 4
```
Even if we index our table on `(created_at, id)` columns, some database engines will still perform at least full index scan to get to the items we need. And this is the primary use case for tuple comparison optimization. If we enable optimization, our code would look something like this:
```go
paginator.New(
paginator.WithKeys([]string{"CreatedAt", "ID"}),
paginator.WithAfter(after),
paginator.WithLimit(3),
paginator.WithAllowTupleCmp(paginate.TRUE),
).Paginate(db, &result)
```
The query that hits our database now looks something like this:
```sql
SELECT *
FROM orders
WHERE (orders.created_at, orders.id) > ($1, $2)
ORDER BY orders.created_at ASC, orders.id ASC
LIMIT 4
```
In this case, if we have index on `(created_at, id)` columns, most DB engines will know how to optimize this query into a simple initial index lookup + scan, making cursor overhead negligible.
### paginator.Rule
- `Key`: Field name in target model struct.
- `Order`: Order for this key only.
- `SQLRepr`: SQL representation used in raw SQL query.
> This is especially useful when you have `JOIN` or table alias in your SQL query. If `SQLRepr` is not specified, paginator will get table name from model, plus table key derived by below rules to form the SQL query:
> 1. Find GORM tag `column` on struct field.
> 2. If tag not found, convert struct field name to snake case.
- `SQLType`: SQL type used for type casting in the raw SQL query.
> This is especially useful when working with custom types (e.g. JSON).
- `NULLReplacement`(v2.2.0): Replacement for NULL value when paginating by nullable column.
> If you paginate by nullable column, you will encounter [NULLS { FIRST | LAST } problems](https://learnsql.com/blog/how-to-order-rows-with-nulls/). This option let you decide how to order rows with NULL value. For instance, we can set this value to `1970-01-01` for a nullable `date` column, to ensure rows with NULL date will be placed at head when order is ASC, or at tail when order is DESC.
- `CustomType`: Extra information needed only when paginating across custom types (e.g. JSON). To support custom type pagination, the type needs to implement the `CustomType` interface:
```go
type CustomType interface {
// GetCustomTypeValue returns the value corresponding to the meta attribute inside the custom type.
GetCustomTypeValue(meta interface{}) (interface{}, error)
}
```
and provide the following information:
- `Meta`: meta attribute inside the custom type. The paginator will pass this meta attribute to the `GetCustomTypeValue` function, which should return the actual value corresponding to the meta attribute. For JSON, meta would contain the JSON key of the element inside JSON to be used for pagination.
- `Type`: GoLang type of the meta attribute.
Also, when paginating across custom types, it is expected that the `SQLRepr` & `SQLType` are set. `SQLRepr` should contain the SQL query to get the meta attribute value, while `SQLType` should be used for type casting if needed. Check examples of [JSON custom type](https://github.com/pilagod/gorm-cursor-paginator/blob/c91935c7488bf9907902c8005f429e719cefa96b/paginator/paginator_test.go#L65-L81) and [custom type setting](https://github.com/pilagod/gorm-cursor-paginator/blob/c91935c7488bf9907902c8005f429e719cefa96b/paginator/paginator_paginate_test.go#L567-L617).
## Changelog
### v2.6.1
- Fix slice encoding ([#64](https://github.com/pilagod/gorm-cursor-paginator/pull/64)), credit to [@chrisroberts](https://github.com/chrisroberts).
### v2.6.0
- Add flag `AllowTupleCmp` to enable SQL tuple comparison for performance optimization of composite cursors ([#62](https://github.com/pilagod/gorm-cursor-paginator/pull/62)), credit to [@tadeboro](https://github.com/tadeboro).
### v2.5.0
- Export `GetCursorEncoder` & `GetCursorDecoder` on `paginator.Paginator` ([#59](https://github.com/pilagod/gorm-cursor-paginator/issues/59)).
### v2.4.2
- Support `NULLReplacement` for custom types ([#58](https://github.com/pilagod/gorm-cursor-paginator/pull/58)), credit to [@zitnik](https://github.com/zitnik).
### v2.4.1
- Cast `NULLReplacement` when `SQLType` is specified ([#52](https://github.com/pilagod/gorm-cursor-paginator/pull/52)), credit to [@jpugliesi](https://github.com/jpugliesi).
### v2.4.0
- Support [NamingStrategy](https://gorm.io/docs/gorm_config.html#NamingStrategy) ([#49](https://github.com/pilagod/gorm-cursor-paginator/pull/49)), credit to [@goxiaoy](https://github.com/goxiaoy).
### v2.3.0
- Add `CustomType` to `paginator.Rule` to support [custom data types](https://gorm.io/docs/data_types.html), credit to [@nikicc](https://github.com/nikicc).
> There are some adjustments to the signatures of `cursor.NewEncoder` and `cursor.NewDecoder`. Be careful when upgrading if you use them directly.
### v2.2.0
- Add `NULLReplacement` to `paginator.Rule` to overcome [NULLS { FIRST | LAST } problems](https://learnsql.com/blog/how-to-order-rows-with-nulls/), credit to [@nikicc](https://github.com/nikicc).
### v2.1.0
- Let client control context, suggestion from [@khalilsarwari](https://github.com/khalilsarwari).
### v2.0.1
- Fix order flip bug when paginating backward, credit to [@sylviamoss](https://github.com/sylviamoss).
## License
© Cyan Ho (pilagod), 2018-NOW
Released under the [MIT License](https://github.com/pilagod/gorm-cursor-paginator/blob/master/LICENSE)