106 lines
2.8 KiB
Go
106 lines
2.8 KiB
Go
// Copyright (c) 2025-2026 Probo Inc <hello@getprobo.com>.
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice appear in all copies.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
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// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
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// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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// PERFORMANCE OF THIS SOFTWARE.
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package page
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import (
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"github.com/jackc/pgx/v5"
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)
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type (
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Cursor[T OrderField] struct {
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Size int
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Position Position
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Key *CursorKey
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OrderBy OrderBy[T]
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}
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Position string
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OrderBy[T OrderField] struct {
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Field T
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Direction OrderDirection
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}
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)
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const (
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DefaultCursorSize = 25
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MaxCursorSize = 500
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Tail Position = "TAIL"
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Head Position = "HEAD"
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)
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func NewCursor[T OrderField](size int, from *CursorKey, pos Position, orderBy OrderBy[T]) *Cursor[T] {
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if size <= 0 {
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size = DefaultCursorSize
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} else if size > MaxCursorSize {
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size = MaxCursorSize
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}
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return &Cursor[T]{
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Size: size,
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Key: from,
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Position: pos,
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OrderBy: orderBy,
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}
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}
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func (c *Cursor[T]) SQLFragment() string {
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fieldName := c.OrderBy.Field.Column()
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var orderDirection string
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switch {
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case c.OrderBy.Direction == OrderDirectionAsc && c.Position == Head:
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orderDirection = "ASC"
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case c.OrderBy.Direction == OrderDirectionDesc && c.Position == Head:
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orderDirection = "DESC"
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case c.OrderBy.Direction == OrderDirectionAsc && c.Position == Tail:
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orderDirection = "DESC"
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case c.OrderBy.Direction == OrderDirectionDesc && c.Position == Tail:
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orderDirection = "ASC"
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}
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whereClause := "TRUE"
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if c.Key != nil && orderDirection == "DESC" {
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whereClause = "(" + fieldName + " <= @cursor_field_value) AND NOT (" + fieldName + " = @cursor_field_value AND id > @cursor_id)"
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} else if c.Key != nil && orderDirection == "ASC" {
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whereClause = "(" + fieldName + " >= @cursor_field_value) AND NOT (" + fieldName + " = @cursor_field_value AND id < @cursor_id)"
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}
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orderByClause := fieldName + " " + orderDirection + ", id " + orderDirection
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return whereClause + " ORDER BY " + orderByClause + " LIMIT @cursor_limit"
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}
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func (c *Cursor[T]) SQLArguments() pgx.NamedArgs {
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var size = c.Size
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if c.Key == nil {
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size += 1
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} else {
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size += 2
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}
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arguments := pgx.NamedArgs{
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"cursor_limit": size,
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}
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if c.Key != nil {
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arguments["cursor_id"] = c.Key.ID
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arguments["cursor_field_value"] = c.Key.Value
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}
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return arguments
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}
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