Prepare DESC commands mechanics. This change contains the implementat…

…ion of the DESC command on the REPL. However it does not implement the actual description of all possible BQL plans.

bql/planner/planner.go

@@ -37,6 +37,9 @@ import (
 type Executor interface {
 	// Execute runs the proposed plan for a given statement.
 	Execute(ctx context.Context) (*table.Table, error)
+
+	// String returns a readable description of the execution plan.
+	String() string
 }
 
 // createPlan encapsulates the sequence of instructions that need to be
@@ -64,6 +67,11 @@ func (p *createPlan) Execute(ctx context.Context) (*table.Table, error) {
 	return t, nil
 }
 
+// String returns a readable description of the execution plan.
+func (p *createPlan) String() string {
+	return "not implemented"
+}
+
 // dropPlan encapsulates the sequence of instructions that need to be
 // executed in order to satisfy the execution of a valid drop BQL statement.
 type dropPlan struct {
@@ -89,6 +97,11 @@ func (p *dropPlan) Execute(ctx context.Context) (*table.Table, error) {
 	return t, nil
 }
 
+// String returns a readable description of the execution plan.
+func (p *dropPlan) String() string {
+	return "not implemented"
+}
+
 // insertPlan encapsulates the sequence of instructions that need to be
 // executed in order to satisfy the execution of a valid insert BQL statement.
 type insertPlan struct {
@@ -143,6 +156,11 @@ func (p *insertPlan) Execute(ctx context.Context) (*table.Table, error) {
 	})
 }
 
+// String returns a readable description of the execution plan.
+func (p *insertPlan) String() string {
+	return "not implemented"
+}
+
 // deletePlan encapsulates the sequence of instructions that need to be
 // executed in order to satisfy the execution of a valid delete BQL statement.
 type deletePlan struct {
@@ -161,6 +179,11 @@ func (p *deletePlan) Execute(ctx context.Context) (*table.Table, error) {
 	})
 }
 
+// String returns a readable description of the execution plan.
+func (p *deletePlan) String() string {
+	return "not implemented"
+}
+
 // queryPlan encapsulates the sequence of instructions that need to be
 // executed in order to satisfy the execution of a valid query BQL statement.
 type queryPlan struct {
@@ -615,6 +638,11 @@ func (p *queryPlan) Execute(ctx context.Context) (*table.Table, error) {
 	return p.tbl, nil
 }
 
+// String returns a readable description of the execution plan.
+func (p *queryPlan) String() string {
+	return "not implemented"
+}
+
 // New create a new executable plan given a semantic BQL statement.
 func New(ctx context.Context, store storage.Store, stm *semantic.Statement, chanSize int) (Executor, error) {
 	switch stm.Type() {

bql/semantic/semantic.go

@@ -84,6 +84,11 @@ type Statement struct {
 	lookupOptions             storage.LookupOptions
 }
 
+// String returns a readable representaion of a statement.
+func (s *Statement) String() string {
+	return ""
+}
+
 // GraphClause represents a clause of a graph pattern in a where clause.
 type GraphClause struct {
 	S          *node.Node
@@ -120,6 +125,11 @@ type GraphClause struct {
 	OTemporal        bool
 }
 
+// String returns a readable representaion of a graph clause.
+func (c *GraphClause) String() string {
+	return ""
+}
+
 // Specificity return
 func (c *GraphClause) Specificity() int {
 	s := 0

tools/vcli/bw/repl/repl.go

@@ -123,6 +123,18 @@ func REPL(driver storage.Store, input *os.File, rl ReadLiner, chanSize, bulkSize
 			l = ""
 			continue
 		}
+		if strings.HasPrefix(l, "desc") {
+			pln, err := planBQL(ctx, l[4:], driver, chanSize)
+			if err != nil {
+				fmt.Printf("[ERROR] %s\n\n", err)
+			} else {
+				fmt.Println(pln.String())
+				fmt.Println("[OK]")
+			}
+			fmt.Print(prompt)
+			l = ""
+			continue
+		}
 		if strings.HasPrefix(l, "run") {
 			path, cmds, err := runBQLFromFile(ctx, driver, chanSize, strings.TrimSpace(l[:len(l)-1]))
 			if err != nil {
@@ -154,6 +166,7 @@ func REPL(driver storage.Store, input *os.File, rl ReadLiner, chanSize, bulkSize
 func printHelp() {
 	fmt.Println("help                                                  - prints help for the bw console.")
 	fmt.Println("export <graph_names_separated_by_commas> <file_path>  - dumps triples from graphs into a file path.")
+	fmt.Println("desc <BQL>                                            - prints the execution plan for a BQL statement.")
 	fmt.Println("load <file_path> <graph_names_separated_by_commas>    - load triples into the specified graphs.")
 	fmt.Println("run <file_with_bql_statements>                        - runs all the BQL statements in the file.")
 	fmt.Println("quit                                                  - quits the console.")
@@ -184,6 +197,19 @@ func runBQLFromFile(ctx context.Context, driver storage.Store, chanSize int, lin
 
 // runBQL attempts to execute the provided query against the given store.
 func runBQL(ctx context.Context, bql string, s storage.Store, chanSize int) (*table.Table, error) {
+	pln, err := planBQL(ctx, bql, s, chanSize)
+	if err != nil {
+		return nil, err
+	}
+	res, err := pln.Execute(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("planner.Execute: failed to execute insert plan with error %v", err)
+	}
+	return res, nil
+}
+
+// planBQL attempts to create the excecution plan for the provided query against the given store.
+func planBQL(ctx context.Context, bql string, s storage.Store, chanSize int) (planner.Executor, error) {
 	p, err := grammar.NewParser(grammar.SemanticBQL())
 	if err != nil {
 		return nil, fmt.Errorf("failed to initilize a valid BQL parser")
@@ -196,9 +222,5 @@ func runBQL(ctx context.Context, bql string, s storage.Store, chanSize int) (*ta
 	if err != nil {
 		return nil, fmt.Errorf("should have not failed to create a plan using memory.DefaultStorage for statement %v with error %v", stm, err)
 	}
-	res, err := pln.Execute(ctx)
-	if err != nil {
-		return nil, fmt.Errorf("planner.Execute: failed to execute insert plan with error %v", err)
-	}
-	return res, nil
+	return pln, nil
 }