// Execute applies a dml sql select expression to the specified context's
//
// writeContext in the case of sql query is similar to a recordset for selects,
// or for delete, insert, update it is like the storage layer
//
func (m *SqlVm) ExecuteSelect(writeContext datasource.ContextWriter, readContext datasource.ContextReader) (err error) {
//defer errRecover(&err)
s := &State{
ExprVm: m,
ContextReader: readContext,
}
s.rv = reflect.ValueOf(s)
// Check and see if we are where Guarded
if m.sel.Where != nil {
//u.Debugf("Has a Where: %v", m.Request.Where.Root.StringAST())
whereValue, ok := s.Walk(m.sel.Where)
if !ok {
return SqlEvalError
}
switch whereVal := whereValue.(type) {
case value.BoolValue:
if whereVal == value.BoolValueFalse {
u.Debugf("Filtering out")
return nil
}
}
//u.Debugf("Matched where: %v", whereValue)
}
for _, col := range m.sel.Columns {
if col.Guard != nil {
// TODO: evaluate if guard
}
if col.Star {
for k, v := range readContext.Row() {
writeContext.Put(&expr.Column{As: k}, nil, v)
}
} else {
//u.Debugf("tree.Root: as?%v %#v", col.As, col.Tree.Root)
v, ok := s.Walk(col.Tree.Root)
if ok {
writeContext.Put(col, readContext, v)
}
}
}
//writeContext.Put()
return
}
