118 lines
2.8 KiB
Go
118 lines
2.8 KiB
Go
package squirrel
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import (
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"bytes"
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"errors"
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"github.com/lann/builder"
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)
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func init() {
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builder.Register(CaseBuilder{}, caseData{})
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}
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// sqlizerBuffer is a helper that allows to write many Sqlizers one by one
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// without constant checks for errors that may come from Sqlizer
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type sqlizerBuffer struct {
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bytes.Buffer
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args []interface{}
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err error
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}
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// WriteSql converts Sqlizer to SQL strings and writes it to buffer
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func (b *sqlizerBuffer) WriteSql(item Sqlizer) {
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if b.err != nil {
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return
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}
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var str string
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var args []interface{}
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str, args, b.err = item.ToSql()
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if b.err != nil {
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return
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}
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b.WriteString(str)
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b.WriteByte(' ')
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b.args = append(b.args, args...)
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}
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func (b *sqlizerBuffer) ToSql() (string, []interface{}, error) {
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return b.String(), b.args, b.err
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}
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// whenPart is a helper structure to describe SQLs "WHEN ... THEN ..." expression
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type whenPart struct {
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when Sqlizer
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then Sqlizer
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}
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func newWhenPart(when interface{}, then interface{}) whenPart {
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return whenPart{newPart(when), newPart(then)}
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}
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// caseData holds all the data required to build a CASE SQL construct
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type caseData struct {
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What Sqlizer
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WhenParts []whenPart
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Else Sqlizer
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}
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// ToSql implements Sqlizer
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func (d *caseData) ToSql() (sqlStr string, args []interface{}, err error) {
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if len(d.WhenParts) == 0 {
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err = errors.New("case expression must contain at lease one WHEN clause")
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return
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}
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sql := sqlizerBuffer{}
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sql.WriteString("CASE ")
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if d.What != nil {
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sql.WriteSql(d.What)
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}
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for _, p := range d.WhenParts {
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sql.WriteString("WHEN ")
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sql.WriteSql(p.when)
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sql.WriteString("THEN ")
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sql.WriteSql(p.then)
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}
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if d.Else != nil {
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sql.WriteString("ELSE ")
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sql.WriteSql(d.Else)
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}
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sql.WriteString("END")
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return sql.ToSql()
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}
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// CaseBuilder builds SQL CASE construct which could be used as parts of queries.
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type CaseBuilder builder.Builder
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// ToSql builds the query into a SQL string and bound args.
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func (b CaseBuilder) ToSql() (string, []interface{}, error) {
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data := builder.GetStruct(b).(caseData)
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return data.ToSql()
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}
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// what sets optional value for CASE construct "CASE [value] ..."
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func (b CaseBuilder) what(expr interface{}) CaseBuilder {
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return builder.Set(b, "What", newPart(expr)).(CaseBuilder)
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}
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// When adds "WHEN ... THEN ..." part to CASE construct
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func (b CaseBuilder) When(when interface{}, then interface{}) CaseBuilder {
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// TODO: performance hint: replace slice of WhenPart with just slice of parts
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// where even indices of the slice belong to "when"s and odd indices belong to "then"s
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return builder.Append(b, "WhenParts", newWhenPart(when, then)).(CaseBuilder)
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}
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// What sets optional "ELSE ..." part for CASE construct
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func (b CaseBuilder) Else(expr interface{}) CaseBuilder {
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return builder.Set(b, "Else", newPart(expr)).(CaseBuilder)
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}
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