Golang Postgres Query Builder for GraphQL Relay-style Cursor-Based Pagination

pagiantion.go

package filters

import (
	"fmt"

	sq "github.com/Masterminds/squirrel"
)

// Pagination provides parameters for a pagination filter.
type Pagination struct {
	// First specifies a count of the first items to retrieve.
	First int `json:"first"`
	// Last
	Last int `json:"last"`

	// Before specifies a cursor to select items from before.
	Before string `json:"before"`
	// After specifies a cursor to select items after.
	After string `json:"after"`

	// NOTES:
	// When before: cursor is used, the edge closest to cursor must come last in the result edges.
	// @see https://relay.dev/graphql/connections.htm#sec-Edge-order
	//
	// When after: cursor is used, the edge closest to cursor must come first in the result edges.
	// @see https://relay.dev/graphql/connections.htm#sec-Edge-order
}

// Apply pagination clauses to the specified query builder.
func (p Pagination) Apply (builder sq.SelectBuilder) (sq.SelectBuilder, error) {
	if p.Before != "" && p.After != "" {
		return sq.SelectBuilder{}, fmt.Errorf("pagniation before and after cannot both be specified")
	}

	if p.Before != "" {
		builder = builder.Where(sq.Lt{
			"id": p.Before,
		})
	} else if p.After != "" {
		builder = builder.Where(sq.Gt{
			"id": p.After,
		})
	}

	if p.First > 0 || p.Last > 0 {
		if p.First > 0 {
			builder = builder.OrderBy("id DESC", "created_at DESC").
				Limit(uint64(p.First) + 1)
		} else if p.Last > 0 {
			builder = builder.OrderBy("id ASC", "created_at ASC").
				Limit(uint64(p.Last) + 1)
		} else {
			builder = builder.OrderBy("id DESC", "created_at DESC").
				Limit(25)
		}
	}

	return builder, nil
}