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package db
import (
"fmt"
"reflect"
"strings"
)
type DataTable[T any] struct {
TableName string
}
// Creates a query that will get all the objects with the same
func (base *DataTable[T]) GetSimilarFieldsQuery(ref T, fields []string) (string, error) {
var structFields = base.getFieldsMap()
var value = reflect.ValueOf(ref)
var filterMap = make(map[string]any)
for _, v := range fields {
var fieldIndex, exists = structFields[v]
if !exists {
return "", fmt.Errorf("Failed to create a query for the object: there is no such field as %s in %s", v, reflect.TypeFor[T]().Name())
}
filterMap[v] = value.Field(fieldIndex).Interface()
}
return base.formQueryWithFilters(filterMap), nil
}
// Filters are stored as KVP where the field is the key and the value is the filter
func (base *DataTable[T]) formQueryWithFilters(filters map[string]any) string {
if len(filters) == 0 {
return base.formSelectAllQuery()
}
var sb = strings.Builder{}
var baseQuery = base.formSelectAllQuery()
sb.WriteString(strings.TrimRight(baseQuery, ";"))
sb.WriteString(" WHERE (")
var isFirst = true
for k, v := range filters {
if !isFirst {
sb.WriteString(" AND ")
}
sb.WriteString(fmt.Sprintf("%s = ", k))
switch v.(type) {
case string:
sb.WriteString(fmt.Sprintf("'%s'", v))
case int, uint64:
sb.WriteString(fmt.Sprintf("%d", v))
}
isFirst = false
}
sb.WriteString(");")
return sb.String()
}
// Forms a query to get all the fields from database
func (base *DataTable[T]) formSelectAllQuery() string {
var sb = strings.Builder{}
sb.WriteString("SELECT (")
var fields = base.getFields()
for i, v := range fields {
if i != 0 {
sb.WriteString(", ")
}
sb.WriteString(v)
}
sb.WriteString(") FROM ")
sb.WriteString(base.TableName)
sb.WriteString(";")
return sb.String()
}
func (base *DataTable[T]) getFields() []string {
var zero T
var outp = make([]string, 0)
for _, f := range reflect.VisibleFields(reflect.TypeOf(zero)) {
var tag, exists = f.Tag.Lookup("sql")
if exists {
outp = append(outp, tag)
} else {
outp = append(outp, f.Name)
}
}
return outp
}
func (base *DataTable[T]) getFieldsMap() map[string]int {
var zero T
var outp = make(map[string]int)
for i, f := range reflect.VisibleFields(reflect.TypeOf(zero)) {
var tag, exists = f.Tag.Lookup("sql")
if exists {
outp[tag] = i
} else {
outp[f.Name] = i
}
}
return outp
}
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