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util_pagination_cursor.go
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util_pagination_cursor.go
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package ssql
import (
"fmt"
"reflect"
"strconv"
"strings"
)
// GetSQLFieldValuePairs uses cursor params to get 'conditions' using the following rules:
// 1. If the after argument is provided => add cursor-field > after to the WHERE clause.
// 2. If the before argument is provided => add cursor-field < before to the WHERE clause.
//
// Note:
// - For next steps 3 and 4 check function 'MutateParamsByCursor'.
// - For next steps 5-10 check function 'PrepareGraphQLConnection'.
func (param CursorParams) getSQLFieldValuePairs(arg *SQLQueryOptions) *ConditionPair {
if (param.After == nil && param.Before == nil) || arg.MainSortField == "" {
return nil
}
comparisonOp := OPGreater
var iterator int = 0
if param.After != nil && CursorToInt(*param.After) > 0 {
comparisonOp = OPGreater
iterator = CursorToInt(*param.After)
} else if param.Before != nil && CursorToInt(*param.Before) > 0 {
comparisonOp = OPLess
iterator = CursorToInt(*param.Before)
}
if arg.MainSortDirection == DirectionDesc {
if comparisonOp == OPGreater {
comparisonOp = OPLess
} else {
comparisonOp = OPGreater
}
}
fvp := &ConditionPair{
Field: arg.MainSortField,
Op: comparisonOp,
Value: iterator,
}
return fvp
}
// CursorParams is the cursor pagination used by GraphQL usually.
// 'after': Returns the elements in the list that come after the specified cursor.
// 'before': Returns the elements in the list that come before the specified cursor.
// 'first': Returns the first n elements from the list.
// 'last': Returns the last n elements from the list.
type CursorParams struct {
After *string `json:"after" query:"after"`
Before *string `json:"before" query:"before"`
First *int `json:"first" query:"first"`
Last *int `json:"last" query:"last"`
}
func CursorToInt(cursor string) int {
origin, err := base64Decode(cursor)
if err != nil {
return 0
}
parts := strings.Split(origin, ":")
if len(parts) < 2 {
return 0
}
c, err := strconv.Atoi(parts[1])
if err != nil {
return 0
}
return c
}
func StrToCursor(cursor interface{}) string {
v := reflect.ValueOf(cursor)
if v.Kind() == reflect.Ptr {
v = v.Elem()
}
switch v.Kind() {
case reflect.Int, reflect.Int8, reflect.Int32, reflect.Int64:
return base64Encode(fmt.Sprintf("c:%d", v.Int()))
case reflect.Uint, reflect.Uint8, reflect.Uint32, reflect.Uint64:
return base64Encode(fmt.Sprintf("c:%d", v.Uint()))
case reflect.String:
return base64Encode(fmt.Sprintf("c:%s", v.String()))
case reflect.Float32, reflect.Float64:
return base64Encode(fmt.Sprintf("c:%b", v.Float()))
}
return base64Encode(fmt.Sprintf("c:%+v", cursor))
}