/
trigger.go
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/
trigger.go
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// Copyright 2020-2021 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package plan
import (
"io"
"github.com/dolthub/go-mysql-server/sql/expression"
"github.com/dolthub/go-mysql-server/sql"
)
type TriggerEvent string
const (
InsertTrigger TriggerEvent = "insert"
UpdateTrigger = "update"
DeleteTrigger = "delete"
)
type TriggerTime string
const (
BeforeTrigger TriggerTime = "before"
AfterTrigger = "after"
)
// TriggerExecutor is node that wraps, or is wrapped by, an INSERT, UPDATE, or DELETE node to execute defined trigger
// logic either before or after that operation. When a table has multiple triggers defined, TriggerExecutor nodes can
// wrap each other as well.
type TriggerExecutor struct {
BinaryNode // Left = wrapped node, Right = trigger execution logic
TriggerEvent TriggerEvent
TriggerTime TriggerTime
TriggerDefinition sql.TriggerDefinition
}
func NewTriggerExecutor(child, triggerLogic sql.Node, triggerEvent TriggerEvent, triggerTime TriggerTime, triggerDefinition sql.TriggerDefinition) *TriggerExecutor {
return &TriggerExecutor{
BinaryNode: BinaryNode{
left: child,
right: triggerLogic,
},
TriggerEvent: triggerEvent,
TriggerTime: triggerTime,
TriggerDefinition: triggerDefinition,
}
}
func (t *TriggerExecutor) String() string {
pr := sql.NewTreePrinter()
_ = pr.WriteNode("Trigger(%s)", t.TriggerDefinition.CreateStatement)
_ = pr.WriteChildren(t.left.String())
return pr.String()
}
func (t *TriggerExecutor) DebugString() string {
pr := sql.NewTreePrinter()
_ = pr.WriteNode("Trigger(%s)", t.TriggerDefinition.CreateStatement)
_ = pr.WriteChildren(sql.DebugString(t.left), sql.DebugString(t.right))
return pr.String()
}
func (t *TriggerExecutor) Schema() sql.Schema {
return t.left.Schema()
}
func (t *TriggerExecutor) WithChildren(children ...sql.Node) (sql.Node, error) {
if len(children) != 2 {
return nil, sql.ErrInvalidChildrenNumber.New(t, len(children), 2)
}
return NewTriggerExecutor(children[0], children[1], t.TriggerEvent, t.TriggerTime, t.TriggerDefinition), nil
}
type triggerIter struct {
child sql.RowIter
executionLogic sql.Node
triggerTime TriggerTime
triggerEvent TriggerEvent
ctx *sql.Context
}
// prependRowInPlanForTriggerExecution returns a transformation function that prepends the row given to any row source in a query
// plan. Any source of rows, as well as any node that alters the schema of its children, will be wrapped so that its
// result rows are prepended with the row given.
func prependRowInPlanForTriggerExecution(row sql.Row) func(c TransformContext) (sql.Node, error) {
return func(c TransformContext) (sql.Node, error) {
switch n := c.Node.(type) {
case *Project:
// Only prepend rows for projects that aren't the input to inserts and other triggers
switch c.Parent.(type) {
case *InsertInto, *TriggerExecutor:
return n, nil
default:
return &prependNode{
UnaryNode: UnaryNode{Child: n},
row: row,
}, nil
}
case *ResolvedTable, *IndexedTableAccess:
return &prependNode{
UnaryNode: UnaryNode{Child: n},
row: row,
}, nil
default:
return n, nil
}
}
}
func (t *triggerIter) Next() (row sql.Row, returnErr error) {
childRow, err := t.child.Next()
if err != nil {
return nil, err
}
// Wrap the execution logic with the current child row before executing it.
logic, err := TransformUpCtx(t.executionLogic, nil, prependRowInPlanForTriggerExecution(childRow))
if err != nil {
return nil, err
}
// We don't do anything interesting with this subcontext yet, but it's a good idea to cancel it independently of the
// parent context if something goes wrong in trigger execution.
ctx, cancelFunc := t.ctx.NewSubContext()
defer cancelFunc()
logicIter, err := logic.RowIter(ctx, childRow)
if err != nil {
return nil, err
}
defer func() {
err := logicIter.Close(t.ctx)
if returnErr == nil {
returnErr = err
}
}()
var logicRow sql.Row
for {
row, err := logicIter.Next()
if err == io.EOF {
break
}
if err != nil {
return nil, err
}
logicRow = row
}
// For some logic statements, we want to return the result of the logic operation as our row, e.g. a Set that alters
// the fields of the new row
if ok, returnRow := shouldUseLogicResult(logic, logicRow); ok {
return returnRow, nil
}
return childRow, nil
}
func shouldUseLogicResult(logic sql.Node, row sql.Row) (bool, sql.Row) {
if qp, ok := logic.(*QueryProcess); ok {
logic = qp.Child
}
switch logic := logic.(type) {
// TODO: are there other statement types that we should use here?
case *Set:
hasSetField := false
for _, expr := range logic.Exprs {
sql.Inspect(expr.(*expression.SetField).Left, func(e sql.Expression) bool {
if _, ok := e.(*expression.GetField); ok {
hasSetField = true
return false
}
return true
})
}
return hasSetField, row[len(row)/2:]
case *TriggerBeginEndBlock:
hasSetField := false
Inspect(logic, func(n sql.Node) bool {
set, ok := n.(*Set)
if !ok {
return true
}
for _, expr := range set.Exprs {
sql.Inspect(expr.(*expression.SetField).Left, func(e sql.Expression) bool {
if _, ok := e.(*expression.GetField); ok {
hasSetField = true
return false
}
return true
})
}
return !hasSetField
})
return hasSetField, row
default:
return false, nil
}
}
func (t *triggerIter) Close(ctx *sql.Context) error {
return t.child.Close(ctx)
}
func (t *TriggerExecutor) RowIter(ctx *sql.Context, row sql.Row) (sql.RowIter, error) {
childIter, err := t.left.RowIter(ctx, row)
if err != nil {
return nil, err
}
return &triggerIter{
child: childIter,
triggerTime: t.TriggerTime,
triggerEvent: t.TriggerEvent,
executionLogic: t.right,
ctx: ctx,
}, nil
}