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package database
// References tracks the references to rows from other rows at specific
// locations in the schema.
type References map[ReferenceSpec]Reference
// ReferenceSpec specifies details about where in the schema a reference occurs.
type ReferenceSpec struct {
// ToTable is the table of the row to which the reference is made
ToTable string
// FromTable is the table of the row from which the reference is made
FromTable string
// FromColumn is the column of the row from which the reference is made
FromColumn string
// FromValue flags if the reference is made on a map key or map value when
// the column is a map
FromValue bool
}
// Reference maps the UUIDs of rows to which the reference is made to the
// rows it is made from
type Reference map[string][]string
// GetReferences gets references to a row
func (rs References) GetReferences(table, uuid string) References {
refs := References{}
for spec, values := range rs {
if spec.ToTable != table {
continue
}
if _, ok := values[uuid]; ok {
refs[spec] = Reference{uuid: values[uuid]}
}
}
return refs
}
// UpdateReferences updates the references with the provided ones. Dangling
// references, that is, the references of rows that are no longer referenced
// from anywhere, are cleaned up.
func (rs References) UpdateReferences(other References) {
for spec, otherRefs := range other {
for to, from := range otherRefs {
rs.updateReference(spec, to, from)
}
}
}
// updateReference updates the references to a row at a specific location in the
// schema
func (rs References) updateReference(spec ReferenceSpec, to string, from []string) {
thisRefs, ok := rs[spec]
if !ok && len(from) > 0 {
// add references from a previously untracked location
rs[spec] = Reference{to: from}
return
}
if len(from) > 0 {
// replace references to this row at this specific location
thisRefs[to] = from
return
}
// otherwise remove previously tracked references
delete(thisRefs, to)
if len(thisRefs) == 0 {
delete(rs, spec)
}
}
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