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refactor(psql_pagination.go): optimize pagination info using Count with Limit(1) #54

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merged 3 commits into from
Jan 4, 2024
Merged

refactor(psql_pagination.go): optimize pagination info using Count with Limit(1) #54

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7755da7
refactor(psql_pagination.go): optimize pagination info using Count wi…
jorgepurposeinplay Jan 1, 2024
7c1d329
fix(psql_pagination.go): make it efficient replacing count with exist…
jorgepurposeinplay Jan 4, 2024
50dd29d
refactor(psql_pagination.go): small simplification
jorgepurposeinplay Jan 4, 2024
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185 changes: 110 additions & 75 deletions pagination/psql_pagination.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ import (
"context"
"fmt"
"slices"
"time"

"gorm.io/gorm"
)
Expand Down Expand Up @@ -47,11 +48,6 @@ func (p PSQLPaginator[T]) ListItems(

pageInfoSession := p.DB.Session(&gorm.Session{}).Model(model)

pageInfo, err := getPageInfo(pageInfoSession, int64(len(items)), paginationParams)
if err != nil {
return nil, PageInfo{}, fmt.Errorf("get page info: %w", err)
}

paginatedItems := make([]PaginatedItem[T], len(items))

for i := range items {
Expand All @@ -66,9 +62,29 @@ func (p PSQLPaginator[T]) ListItems(
}
}

var (
startCursor *string
endCursor *string
)

if len(paginatedItems) > 0 {
pageInfo.StartCursor = &paginatedItems[0].Cursor
pageInfo.EndCursor = &paginatedItems[len(paginatedItems)-1].Cursor
startCursor = &paginatedItems[0].Cursor
endCursor = &paginatedItems[len(paginatedItems)-1].Cursor
}

pageInfo, err := getPageInfo[T](
pageInfoSession,
paginationParams,
startCursor,
endCursor,
)
if err != nil {
return nil, PageInfo{}, fmt.Errorf("get page info: %w", err)
}

if len(paginatedItems) > 0 {
pageInfo.StartCursor = startCursor
pageInfo.EndCursor = endCursor
}

return paginatedItems, pageInfo, nil
Expand Down Expand Up @@ -110,120 +126,139 @@ func queryItems[T any](ses *gorm.DB, pagination Arguments) ([]T, error) {
return items, nil
}

func getPageInfo(
func getPageInfo[T any](
db *gorm.DB,
itemsCount int64,
pagination Arguments,
startCursor *string,
endCursor *string,
) (PageInfo, error) {
if pagination.First != nil {
return getForwardPaginationPageInfo(db, itemsCount, pagination)
return getForwardPaginationPageInfo[T](db, pagination, endCursor)
}

return getBackwardPaginationPageInfo(db, itemsCount, pagination)
return getBackwardPaginationPageInfo[T](db, pagination, startCursor)
}

func getForwardPaginationPageInfo(
func getForwardPaginationPageInfo[T any](
db *gorm.DB,
itemsCount int64,
pagination Arguments,
endCursor *string,
) (PageInfo, error) {
var (
totalItemsForward int64
totalItemsBackward int64
hasItemForward bool
hasItemBackward bool
)

totalItemsForwardQuery := db.
Session(&gorm.Session{}).
Order("created_at DESC")
var pageInfo PageInfo

totalItemsBackwardQuery := db.
Session(&gorm.Session{}).
Order("created_at DESC")
createdAt := time.Now()

if pagination.afterCursor == nil {
if err := totalItemsForwardQuery.Count(&totalItemsForward).Error; err != nil {
return PageInfo{}, fmt.Errorf("count items for forward pagination: %w", err)
if endCursor != nil {
ca, err := time.Parse(time.RFC3339Nano, *endCursor)
if err != nil {
return PageInfo{}, fmt.Errorf("parse end cursor: %w", err)
}

return PageInfo{
HasPreviousPage: false,
HasNextPage: totalItemsForward > itemsCount,
}, nil
createdAt = ca
} else if pagination.afterCursor != nil {
// Case where zero items are fetched but with a cursor.
createdAt = pagination.afterCursor.CreatedAt
}

totalItemsForwardQuery = totalItemsForwardQuery.Where(
"created_at < ?",
pagination.afterCursor.CreatedAt,
)
var model T

totalItemsBackwardQuery = totalItemsBackwardQuery.Debug().Where(
"created_at > ?",
pagination.afterCursor.CreatedAt,
stmt := &gorm.Statement{DB: db}
if err := stmt.Parse(&model); err != nil {
return PageInfo{}, fmt.Errorf("parse model: %w", err)
}

tableName := stmt.Schema.Table

query := fmt.Sprintf(
"SELECT EXISTS(SELECT 1 FROM %s WHERE created_at < ?)", tableName,
)
if err := db.Raw(query, createdAt).Scan(&hasItemForward).Error; err != nil {
return PageInfo{}, fmt.Errorf("existence check for forward pagination: %w", err)
}

pageInfo.HasNextPage = hasItemForward

if err := totalItemsForwardQuery.Count(&totalItemsForward).Error; err != nil {
return PageInfo{}, fmt.Errorf("count items for forward pagination: %w", err)
if pagination.afterCursor == nil {
pageInfo.HasPreviousPage = false
return pageInfo, nil
}

if err := totalItemsBackwardQuery.Count(&totalItemsBackward).Error; err != nil {
return PageInfo{}, fmt.Errorf("count items for backward pagination: %w", err)
query = fmt.Sprintf(
"SELECT EXISTS(SELECT 1 FROM %s WHERE created_at > ?)", tableName,
)
if err := db.Raw(query, pagination.afterCursor.CreatedAt).
Scan(&hasItemBackward).Error; err != nil {
return PageInfo{}, fmt.Errorf("existence check for backward pagination: %w", err)
}

return PageInfo{
HasPreviousPage: totalItemsBackward > 0,
HasNextPage: totalItemsForward > itemsCount,
}, nil
pageInfo.HasPreviousPage = hasItemBackward

return pageInfo, nil
}

func getBackwardPaginationPageInfo(
func getBackwardPaginationPageInfo[T any](
db *gorm.DB,
itemsCount int64,
pagination Arguments,
startCursor *string,
) (PageInfo, error) {
var (
totalItemsForward int64
totalItemsBackward int64
hasItemForward bool
hasItemBackward bool
)

totalItemsForwardQuery := db.
Session(&gorm.Session{}).
Order("created_at DESC")
var pageInfo PageInfo

totalItemsBackwardQuery := db.
Session(&gorm.Session{}).
Order("created_at DESC")
var createdAt time.Time

if pagination.Before == nil {
if err := totalItemsBackwardQuery.Count(&totalItemsBackward).Error; err != nil {
return PageInfo{}, fmt.Errorf("count items for backward pagination: %w", err)
if startCursor != nil {
ca, err := time.Parse(time.RFC3339Nano, *startCursor)
if err != nil {
return PageInfo{}, fmt.Errorf("parse start cursor: %w", err)
}

return PageInfo{
HasPreviousPage: totalItemsBackward > itemsCount,
HasNextPage: false,
}, nil
createdAt = ca
} else if pagination.beforeCursor != nil {
// Case where zero items are fetched but with a cursor.
createdAt = pagination.beforeCursor.CreatedAt
}

totalItemsForwardQuery = totalItemsForwardQuery.Where(
"created_at < ?",
pagination.beforeCursor.CreatedAt,
)
var model T

stmt := &gorm.Statement{DB: db}
if err := stmt.Parse(&model); err != nil {
return PageInfo{}, fmt.Errorf("parse model: %w", err)
}

tableName := stmt.Schema.Table

totalItemsBackwardQuery = totalItemsBackwardQuery.Where(
"created_at > ?",
pagination.beforeCursor.CreatedAt,
query := fmt.Sprintf(
"SELECT EXISTS(SELECT 1 FROM %s WHERE created_at > ?)", tableName,
)
if err := db.Raw(query, createdAt).Scan(&hasItemBackward).Error; err != nil {
return PageInfo{}, fmt.Errorf("existence check for backward pagination: %w", err)
}

pageInfo.HasPreviousPage = hasItemBackward

if err := totalItemsForwardQuery.Count(&totalItemsForward).Error; err != nil {
return PageInfo{}, fmt.Errorf("count items for forward pagination: %w", err)
if pagination.beforeCursor == nil {
pageInfo.HasNextPage = false
return pageInfo, nil
}

if err := totalItemsBackwardQuery.Count(&totalItemsBackward).Error; err != nil {
return PageInfo{}, fmt.Errorf("count items for backward pagination: %w", err)
query = fmt.Sprintf(
"SELECT EXISTS(SELECT 1 FROM %s WHERE created_at < ?)", tableName,
)
if err := db.Raw(query, pagination.beforeCursor.CreatedAt).
Scan(&hasItemForward).Error; err != nil {
return PageInfo{}, fmt.Errorf("existence check for forward pagination: %w", err)
}

return PageInfo{
HasPreviousPage: totalItemsBackward > itemsCount,
HasNextPage: totalItemsForward > 0,
}, nil
pageInfo.HasNextPage = hasItemForward

return pageInfo, nil
}
88 changes: 85 additions & 3 deletions pagination/psql_pagination_test.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -29,10 +29,10 @@ func TestListPSQLPaginatedItems(t *testing.T) {

const schema = `
CREATE TABLE users (
id UUID PRIMARY KEY,
name TEXT,
id UUID PRIMARY KEY,
name TEXT,
created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW()
);
);
`

psqlContainer := psqldocker.NewContainer(
Expand Down Expand Up @@ -192,6 +192,88 @@ func TestListPSQLPaginatedItems(t *testing.T) {
EndCursor: userToCursor(users[94]),
},
},
"First0NoCursor": {
params: pagination.Arguments{
First: ptr.To(0),
},
expectedError: require.NoError,
expectedUsers: []user{},
expectedPageInfo: pagination.PageInfo{
HasPreviousPage: false,
HasNextPage: true,
StartCursor: nil,
EndCursor: nil,
},
},
"Last0NoCursor": {
params: pagination.Arguments{
Last: ptr.To(0),
},
expectedError: require.NoError,
expectedUsers: []user{},
expectedPageInfo: pagination.PageInfo{
HasPreviousPage: true,
HasNextPage: false,
StartCursor: nil,
EndCursor: nil,
},
},
"First0WithCursor": {
params: pagination.Arguments{
First: ptr.To(0),
After: userToCursor(users[0]),
},
expectedError: require.NoError,
expectedUsers: []user{},
expectedPageInfo: pagination.PageInfo{
HasPreviousPage: false,
HasNextPage: true,
StartCursor: nil,
EndCursor: nil,
},
},
"Last0WithCursor": {
params: pagination.Arguments{
Last: ptr.To(0),
Before: userToCursor(users[99]),
},
expectedError: require.NoError,
expectedUsers: []user{},
expectedPageInfo: pagination.PageInfo{
HasPreviousPage: true,
HasNextPage: false,
StartCursor: nil,
EndCursor: nil,
},
},
"First0CursorAtEnd": {
params: pagination.Arguments{
First: ptr.To(0),
After: userToCursor(users[99]),
},
expectedError: require.NoError,
expectedUsers: []user{},
expectedPageInfo: pagination.PageInfo{
HasPreviousPage: true,
HasNextPage: false,
StartCursor: nil,
EndCursor: nil,
},
},
"Last0CursorStart": {
params: pagination.Arguments{
Last: ptr.To(0),
Before: userToCursor(users[0]),
},
expectedError: require.NoError,
expectedUsers: []user{},
expectedPageInfo: pagination.PageInfo{
HasPreviousPage: false,
HasNextPage: true,
StartCursor: nil,
EndCursor: nil,
},
},
}

for name, test := range tests {
Expand Down
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