Function buildUpsertQuery

edgraph/server.go:874–921

buildUpsertQuery modifies the query to evaluate the @if condition defined in Conditional Upsert.

(qc *queryContext)

// buildUpsertQuery modifies the query to evaluate the
// @if condition defined in Conditional Upsert.
func buildUpsertQuery(qc *queryContext) (string, error) {
	if qc.req.Query == "" || len(qc.gmuList) == 0 {
		return qc.req.Query, nil
	}

	qc.condVars = make([]string, len(qc.req.Mutations))

	var upsertQB strings.Builder
	x.Check2(upsertQB.WriteString(strings.TrimSuffix(qc.req.Query, "}")))

	for i, gmu := range qc.gmuList {
		isCondUpsert := strings.TrimSpace(gmu.Cond) != ""
		if isCondUpsert {
			if err := validateCondValue(gmu.Cond); err != nil {
				return "", err
			}

			qc.condVars[i] = fmt.Sprintf("__dgraph_upsertcheck_%v__", strconv.Itoa(i))
			qc.uidRes[qc.condVars[i]] = nil
			// @if in upsert is same as @filter in the query
			cond := strings.Replace(gmu.Cond, "@if", "@filter", 1)

			// Add dummy query to evaluate the @if directive, ok to use uid(0) because
			// dgraph doesn't check for existence of UIDs until we query for other predicates.
			// Here, we are only querying for uid predicate in the dummy query.
			//
			// For example if - mu.Query = {
			//      me(...) {...}
			//   }
			//
			// Then, upsertQuery = {
			//      me(...) {...}
			//      __dgraph_0__ as var(func: uid(0)) @filter(...)
			//   }
			//
			// The variable __dgraph_0__ will -
			//      * be empty if the condition is true
			//      * have 1 UID (the 0 UID) if the condition is false
			x.Check2(upsertQB.WriteString(qc.condVars[i]))
			x.Check2(upsertQB.WriteString(` as var(func: uid(0)) `))
			x.Check2(upsertQB.WriteString(cond))
			x.Check2(upsertQB.WriteString("\n"))
		}
	}

	x.Check2(upsertQB.WriteString(`}`))
	return upsertQB.String(), nil
}

// updateMutations updates the mutation and replaces uid(var) and val(var) with
// their values or a blank node, in case of an upsert.