postgres.*Watch.getChanges - Code Metrics - Inspection of "Merge pull request #1706 from Permify/ufuk/watchap..." - Permify/permify - Measure and Improve Code Quality continuously with Scrutinizer

Passed

Push — master ( 92321d...fd0104 )

by Tolga

created 2024-10-21 08:07 UTC

postgres.*Watch.getChanges D

↳ Parent: internal/storage/postgres/watch.go

Complexity

Conditions

Size

Total Lines	130
Code Lines	73

Duplication

Lines	0
Ratio	0 %

Importance

Changes

Metric	Value
cc	12
eloc	73
nop	3
dl	0
loc	130
rs	4.2436
c	0
b	0
f	0

How to fix Long Method Complexity

package postgres

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"

	"github.com/golang/protobuf/jsonpb"

	"google.golang.org/protobuf/types/known/anypb"

	"github.com/Masterminds/squirrel"

	"github.com/Permify/permify/internal/storage"
	"github.com/Permify/permify/internal/storage/postgres/snapshot"
	"github.com/Permify/permify/internal/storage/postgres/types"
	db "github.com/Permify/permify/pkg/database/postgres"
	base "github.com/Permify/permify/pkg/pb/base/v1"
)

// Watch is an implementation of the storage.Watch interface, which is used
type Watch struct {
	// database is a pointer to a Postgres database instance, which is used
	// to perform operations on the relationship data.
	database *db.Postgres

	// txOptions holds the configuration for database transactions, such as
	// isolation level and read-only mode, to be applied when performing
	// operations on the relationship data.
	txOptions pgx.TxOptions
}

// NewWatcher returns a new instance of the Watch.
func NewWatcher(database *db.Postgres) *Watch {
	return &Watch{
		database:  database,
		txOptions: pgx.TxOptions{IsoLevel: pgx.ReadCommitted, AccessMode: pgx.ReadOnly},
	}
}

// Watch returns a channel that emits a stream of changes to the relationship tuples in the database.
func (w *Watch) Watch(ctx context.Context, tenantID, snap string) (<-chan *base.DataChanges, <-chan error) {
	// Create channels for changes and errors.
	changes := make(chan *base.DataChanges, w.database.GetWatchBufferSize())
	errs := make(chan error, 1)

	var sleep *time.Timer
	const maxSleepDuration = 2 * time.Second
	const defaultSleepDuration = 100 * time.Millisecond
	sleepDuration := defaultSleepDuration

	slog.DebugContext(ctx, "watching for changes in the database", slog.Any("tenant_id", tenantID), slog.Any("snapshot", snap))

	// Decode the snapshot value.
	// The snapshot value represents a point in the history of the database.
	st, err := snapshot.EncodedToken{Value: snap}.Decode()
	if err != nil {
		// If there is an error in decoding the snapshot, send the error and return.
		errs <- err

		slog.Error("failed to decode snapshot", slog.Any("error", err))

		return changes, errs
	}

	// Start a goroutine to watch for changes in the database.
	go func() {
		// Ensure to close the channels when we're done.
		defer close(changes)
		defer close(errs)

		// Get the transaction ID from the snapshot.
		cr := st.(snapshot.Token).Value.Uint

		// Continuously watch for changes.
		for {
			// Get the list of recent transaction IDs.
			recentIDs, err := w.getRecentXIDs(ctx, cr, tenantID)
			if err != nil {
				// If there is an error in getting recent transaction IDs, send the error and return.

				slog.Error("error getting recent transaction", slog.Any("error", err))

				errs <- err
				return
			}

			// Process each recent transaction ID.
			for _, id := range recentIDs {
				// Get the changes in the database associated with the current transaction ID.
				updates, err := w.getChanges(ctx, id, tenantID)
				if err != nil {
					// If there is an error in getting the changes, send the error and return.
					slog.ErrorContext(ctx, "failed to get changes for transaction", slog.Any("id", id), slog.Any("error", err))
					errs <- err
					return
				}

				// Send the changes, but respect the context cancellation.
				select {
				case <-ctx.Done(): // If the context is done, send an error and return.
					slog.ErrorContext(ctx, "context canceled, stopping watch")
					errs <- errors.New(base.ErrorCode_ERROR_CODE_CANCELLED.String())
					return
				case changes <- updates: // Send updates to the changes channel.
					slog.DebugContext(ctx, "sent updates to the changes channel for transaction", slog.Any("id", id))
				}

				// Update the transaction ID for the next round.
				cr = id.Uint
				sleepDuration = defaultSleepDuration
			}

			if len(recentIDs) == 0 {

				if sleep == nil {
					sleep = time.NewTimer(sleepDuration)
				} else {
					sleep.Reset(sleepDuration)
				}

				// Increase the sleep duration exponentially, but cap it at maxSleepDuration.
				if sleepDuration < maxSleepDuration {
					sleepDuration *= 2
				} else {
					sleepDuration = maxSleepDuration
				}

				select {
				case <-ctx.Done(): // If the context is done, send an error and return.
					slog.ErrorContext(ctx, "context canceled, stopping watch")
					errs <- errors.New(base.ErrorCode_ERROR_CODE_CANCELLED.String())
					return
				case <-sleep.C: // If the timer is done, continue the loop.
					slog.DebugContext(ctx, "no recent transaction IDs, waiting for changes")
				}
			}
		}
	}()

	slog.DebugContext(ctx, "watch started successfully")

	// Return the channels that the caller will listen to for changes and errors.
	return changes, errs
}

// getRecentXIDs fetches a list of XID8 identifiers from the 'transactions' table
// for all transactions committed after a specified XID value.
//
// Parameters:
//   - ctx:       A context to control the execution lifetime.
//   - value:     The transaction XID after which we need the changes.
//   - tenantID:  The ID of the tenant to filter the transactions for.
//
// Returns:
//   - A slice of XID8 identifiers.
//   - An error if the query fails to execute, or other error occurs during its execution.
func (w *Watch) getRecentXIDs(ctx context.Context, value uint64, tenantID string) ([]types.XID8, error) {
	// Convert the value to a string formatted as a Postgresql XID8 type.
	valStr := fmt.Sprintf("'%v'::xid8", value)

	subquery := fmt.Sprintf("(select pg_xact_commit_timestamp(id::xid) from transactions where id = %s)", valStr)

	// Build the main query to get transactions committed after the one with a given XID,
	// still visible in the current snapshot, ordered by their commit timestamps.
	builder := w.database.Builder.Select("id").
		From(TransactionsTable).
		Where(fmt.Sprintf("pg_xact_commit_timestamp(id::xid) > (%s)", subquery)).
		Where("id < pg_snapshot_xmin(pg_current_snapshot())").
		Where(squirrel.Eq{"tenant_id": tenantID}).
		OrderBy("pg_xact_commit_timestamp(id::xid)")

	// Convert the builder to a SQL query and arguments.
	query, args, err := builder.ToSql()
	if err != nil {

		slog.ErrorContext(ctx, "error while building sql query", slog.Any("error", err))

		return nil, err
	}

	slog.DebugContext(ctx, "executing SQL query to get recent transaction", slog.Any("query", query), slog.Any("arguments", args))

	// Execute the SQL query.
	rows, err := w.database.ReadPool.Query(ctx, query, args...)
	if err != nil {
		slog.ErrorContext(ctx, "failed to execute SQL query", slog.Any("error", err))
		return nil, err
	}
	defer rows.Close()

	// Loop through the rows and append XID8 values to the results.
	var xids []types.XID8
	for rows.Next() {
		var xid types.XID8
		err := rows.Scan(&xid)
		if err != nil {
			slog.ErrorContext(ctx, "error while scanning row", slog.Any("error", err))
			return nil, err
		}
		xids = append(xids, xid)
	}

	// Check for errors that could have occurred during iteration.
	err = rows.Err()
	if err != nil {

		slog.ErrorContext(ctx, "failed to iterate over rows", slog.Any("error", err))

		return nil, err
	}

	slog.DebugContext(ctx, "successfully retrieved recent transaction", slog.Any("ids", xids))
	return xids, nil
}

// getChanges is a method that retrieves the changes that occurred in the relation tuples within a specified transaction.
//
// ctx: The context.Context instance for managing the life-cycle of this function.
// value: The ID of the transaction for which to retrieve the changes.
// tenantID: The ID of the tenant for which to retrieve the changes.
//
// This method returns a TupleChanges instance that encapsulates the changes in the relation tuples within the specified
// transaction, or an error if something went wrong during execution.
func (w *Watch) getChanges(ctx context.Context, value types.XID8, tenantID string) (*base.DataChanges, error) {
	// Initialize a new TupleChanges instance.
	changes := &base.DataChanges{}

	slog.DebugContext(ctx, "retrieving changes for transaction", slog.Any("id", value), slog.Any("tenant_id", tenantID))

	// Construct the SQL SELECT statement for retrieving the changes from the RelationTuplesTable.
	tbuilder := w.database.Builder.Select("entity_type, entity_id, relation, subject_type, subject_id, subject_relation, expired_tx_id").
		From(RelationTuplesTable).
		Where(squirrel.Eq{"tenant_id": tenantID}).Where(squirrel.Or{
		squirrel.Eq{"created_tx_id": value},
		squirrel.Eq{"expired_tx_id": value},
	})

	// Generate the SQL query and arguments.
	tquery, targs, err := tbuilder.ToSql()
	if err != nil {
		slog.ErrorContext(ctx, "error while building sql query for relation tuples", slog.Any("error", err))
		return nil, err
	}

	slog.DebugContext(ctx, "executing sql query for relation tuples", slog.Any("query", tquery), slog.Any("arguments", targs))

	// Execute the SQL query and retrieve the result rows.
	var trows pgx.Rows
	trows, err = w.database.ReadPool.Query(ctx, tquery, targs...)
	if err != nil {
		slog.ErrorContext(ctx, "failed to execute sql query for relation tuples", slog.Any("error", err))
		return nil, errors.New(base.ErrorCode_ERROR_CODE_EXECUTION.String())
	}
	// Ensure the rows are closed after processing.
	defer trows.Close()

	abuilder := w.database.Builder.Select("entity_type, entity_id, attribute, value, expired_tx_id").
		From(AttributesTable).
		Where(squirrel.Eq{"tenant_id": tenantID}).Where(squirrel.Or{
		squirrel.Eq{"created_tx_id": value},
		squirrel.Eq{"expired_tx_id": value},
	})

	aquery, aargs, err := abuilder.ToSql()
	if err != nil {
		slog.ErrorContext(ctx, "error while building SQL query for attributes", slog.Any("error", err))
		return nil, err
	}

	slog.DebugContext(ctx, "executing sql query for attributes", slog.Any("query", aquery), slog.Any("arguments", aargs))

	var arows pgx.Rows
	arows, err = w.database.ReadPool.Query(ctx, aquery, aargs...)
	if err != nil {
		slog.ErrorContext(ctx, "error while executing SQL query for attributes", slog.Any("error", err))
		return nil, errors.New(base.ErrorCode_ERROR_CODE_EXECUTION.String())
	}
	// Ensure the rows are closed after processing.
	defer arows.Close()

	// Set the snapshot token for the changes.
	changes.SnapToken = snapshot.Token{Value: value}.Encode().String()

	// Iterate through the result rows.
	for trows.Next() {
		var expiredXID types.XID8

		rt := storage.RelationTuple{}
		// Scan the result row into a RelationTuple instance.
		err = trows.Scan(&rt.EntityType, &rt.EntityID, &rt.Relation, &rt.SubjectType, &rt.SubjectID, &rt.SubjectRelation, &expiredXID)
		if err != nil {
			slog.ErrorContext(ctx, "error while scanning row for relation tuples", slog.Any("error", err))
			return nil, err
		}

		// Determine the operation type based on the expired transaction ID.
		op := base.DataChange_OPERATION_CREATE
		if expiredXID.Uint == value.Uint {
			op = base.DataChange_OPERATION_DELETE
		}

		// Append the change to the list of changes.
		changes.DataChanges = append(changes.DataChanges, &base.DataChange{
			Operation: op,
			Type: &base.DataChange_Tuple{
				Tuple: rt.ToTuple(),
			},
		})
	}

	// Iterate through the result rows.
	for arows.Next() {
		var expiredXID types.XID8

		rt := storage.Attribute{}

		var valueStr string

		// Scan the result row into a RelationTuple instance.
		err = arows.Scan(&rt.EntityType, &rt.EntityID, &rt.Attribute, &valueStr, &expiredXID)
		if err != nil {
			slog.ErrorContext(ctx, "error while scanning row for attributes", slog.Any("error", err))
			return nil, err
		}

		// Unmarshal the JSON data from `valueStr` into `rt.Value`.
		rt.Value = &anypb.Any{}
		unmarshaler := &jsonpb.Unmarshaler{}
		err = unmarshaler.Unmarshal(strings.NewReader(valueStr), rt.Value)
		if err != nil {
			slog.ErrorContext(ctx, "failed to unmarshal attribute value", slog.Any("error", err))
			return nil, err
		}

		// Determine the operation type based on the expired transaction ID.
		op := base.DataChange_OPERATION_CREATE
		if expiredXID.Uint == value.Uint {
			op = base.DataChange_OPERATION_DELETE
		}

		// Append the change to the list of changes.
		changes.DataChanges = append(changes.DataChanges, &base.DataChange{
			Operation: op,
			Type: &base.DataChange_Attribute{
				Attribute: rt.ToAttribute(),
			},
		})
	}

	slog.DebugContext(ctx, "successfully retrieved changes for transaction", slog.Any("id", value))

	// Return the changes and no error.
	return changes, nil
}


1			package postgres
2
3			import (
4			"context"
5			"errors"
6			"fmt"
7			"log/slog"
8			"strings"
9			"time"
10
11			"github.com/jackc/pgx/v5"
12
13			"github.com/golang/protobuf/jsonpb"
14
15			"google.golang.org/protobuf/types/known/anypb"
16
17			"github.com/Masterminds/squirrel"
18
19			"github.com/Permify/permify/internal/storage"
20			"github.com/Permify/permify/internal/storage/postgres/snapshot"
21			"github.com/Permify/permify/internal/storage/postgres/types"
22			db "github.com/Permify/permify/pkg/database/postgres"
23			base "github.com/Permify/permify/pkg/pb/base/v1"
24			)
25
26			// Watch is an implementation of the storage.Watch interface, which is used
27			type Watch struct {
28			// database is a pointer to a Postgres database instance, which is used
29			// to perform operations on the relationship data.
30			database *db.Postgres
31
32			// txOptions holds the configuration for database transactions, such as
33			// isolation level and read-only mode, to be applied when performing
34			// operations on the relationship data.
35			txOptions pgx.TxOptions
36			}
37
38			// NewWatcher returns a new instance of the Watch.
39			func NewWatcher(database db.Postgres) Watch {
40			return &Watch{
41			database: database,
42			txOptions: pgx.TxOptions{IsoLevel: pgx.ReadCommitted, AccessMode: pgx.ReadOnly},
43			}
44			}
45
46			// Watch returns a channel that emits a stream of changes to the relationship tuples in the database.
47			func (w Watch) Watch(ctx context.Context, tenantID, snap string) (<-chan base.DataChanges, <-chan error) {
48			// Create channels for changes and errors.
49			changes := make(chan *base.DataChanges, w.database.GetWatchBufferSize())
50			errs := make(chan error, 1)
51
52			var sleep *time.Timer
53			const maxSleepDuration = 2 * time.Second
54			const defaultSleepDuration = 100 * time.Millisecond
55			sleepDuration := defaultSleepDuration
56
57			slog.DebugContext(ctx, "watching for changes in the database", slog.Any("tenant_id", tenantID), slog.Any("snapshot", snap))
58
59			// Decode the snapshot value.
60			// The snapshot value represents a point in the history of the database.
61			st, err := snapshot.EncodedToken{Value: snap}.Decode()
62			if err != nil {
63			// If there is an error in decoding the snapshot, send the error and return.
64			errs <- err
65
66			slog.Error("failed to decode snapshot", slog.Any("error", err))
67
68			return changes, errs
69			}
70
71			// Start a goroutine to watch for changes in the database.
72			go func() {
73			// Ensure to close the channels when we're done.
74			defer close(changes)
75			defer close(errs)
76
77			// Get the transaction ID from the snapshot.
78			cr := st.(snapshot.Token).Value.Uint
79
80			// Continuously watch for changes.
81			for {
82			// Get the list of recent transaction IDs.
83			recentIDs, err := w.getRecentXIDs(ctx, cr, tenantID)
84			if err != nil {
85			// If there is an error in getting recent transaction IDs, send the error and return.
86
87			slog.Error("error getting recent transaction", slog.Any("error", err))
88
89			errs <- err
90			return
91			}
92
93			// Process each recent transaction ID.
94			for _, id := range recentIDs {
95			// Get the changes in the database associated with the current transaction ID.
96			updates, err := w.getChanges(ctx, id, tenantID)
97			if err != nil {
98			// If there is an error in getting the changes, send the error and return.
99			slog.ErrorContext(ctx, "failed to get changes for transaction", slog.Any("id", id), slog.Any("error", err))
100			errs <- err
101			return
102			}
103
104			// Send the changes, but respect the context cancellation.
105			select {
106			case <-ctx.Done(): // If the context is done, send an error and return.
107			slog.ErrorContext(ctx, "context canceled, stopping watch")
108			errs <- errors.New(base.ErrorCode_ERROR_CODE_CANCELLED.String())
109			return
110			case changes <- updates: // Send updates to the changes channel.
111			slog.DebugContext(ctx, "sent updates to the changes channel for transaction", slog.Any("id", id))
112			}
113
114			// Update the transaction ID for the next round.
115			cr = id.Uint
116			sleepDuration = defaultSleepDuration
117			}
118
119			if len(recentIDs) == 0 {
120
121			if sleep == nil {
122			sleep = time.NewTimer(sleepDuration)
123			} else {
124			sleep.Reset(sleepDuration)
125			}
126
127			// Increase the sleep duration exponentially, but cap it at maxSleepDuration.
128			if sleepDuration < maxSleepDuration {
129			sleepDuration *= 2
130			} else {
131			sleepDuration = maxSleepDuration
132			}
133
134			select {
135			case <-ctx.Done(): // If the context is done, send an error and return.
136			slog.ErrorContext(ctx, "context canceled, stopping watch")
137			errs <- errors.New(base.ErrorCode_ERROR_CODE_CANCELLED.String())
138			return
139			case <-sleep.C: // If the timer is done, continue the loop.
140			slog.DebugContext(ctx, "no recent transaction IDs, waiting for changes")
141			}
142			}
143			}
144			}()
145
146			slog.DebugContext(ctx, "watch started successfully")
147
148			// Return the channels that the caller will listen to for changes and errors.
149			return changes, errs
150			}
151
152			// getRecentXIDs fetches a list of XID8 identifiers from the 'transactions' table
153			// for all transactions committed after a specified XID value.
154			//
155			// Parameters:
156			// - ctx: A context to control the execution lifetime.
157			// - value: The transaction XID after which we need the changes.
158			// - tenantID: The ID of the tenant to filter the transactions for.
159			//
160			// Returns:
161			// - A slice of XID8 identifiers.
162			// - An error if the query fails to execute, or other error occurs during its execution.
163			func (w *Watch) getRecentXIDs(ctx context.Context, value uint64, tenantID string) ([]types.XID8, error) {
164			// Convert the value to a string formatted as a Postgresql XID8 type.
165			valStr := fmt.Sprintf("'%v'::xid8", value)
166
167			subquery := fmt.Sprintf("(select pg_xact_commit_timestamp(id::xid) from transactions where id = %s)", valStr)
168
169			// Build the main query to get transactions committed after the one with a given XID,
170			// still visible in the current snapshot, ordered by their commit timestamps.
171			builder := w.database.Builder.Select("id").
172			From(TransactionsTable).
173			Where(fmt.Sprintf("pg_xact_commit_timestamp(id::xid) > (%s)", subquery)).
174			Where("id < pg_snapshot_xmin(pg_current_snapshot())").
175			Where(squirrel.Eq{"tenant_id": tenantID}).
176			OrderBy("pg_xact_commit_timestamp(id::xid)")
177
178			// Convert the builder to a SQL query and arguments.
179			query, args, err := builder.ToSql()
180			if err != nil {
181
182			slog.ErrorContext(ctx, "error while building sql query", slog.Any("error", err))
183
184			return nil, err
185			}
186
187			slog.DebugContext(ctx, "executing SQL query to get recent transaction", slog.Any("query", query), slog.Any("arguments", args))
188
189			// Execute the SQL query.
190			rows, err := w.database.ReadPool.Query(ctx, query, args...)
191			if err != nil {
192			slog.ErrorContext(ctx, "failed to execute SQL query", slog.Any("error", err))
193			return nil, err
194			}
195			defer rows.Close()
196
197			// Loop through the rows and append XID8 values to the results.
198			var xids []types.XID8
199			for rows.Next() {
200			var xid types.XID8
201			err := rows.Scan(&xid)
202			if err != nil {
203			slog.ErrorContext(ctx, "error while scanning row", slog.Any("error", err))
204			return nil, err
205			}
206			xids = append(xids, xid)
207			}
208
209			// Check for errors that could have occurred during iteration.
210			err = rows.Err()
211			if err != nil {
212
213			slog.ErrorContext(ctx, "failed to iterate over rows", slog.Any("error", err))
214
215			return nil, err
216			}
217
218			slog.DebugContext(ctx, "successfully retrieved recent transaction", slog.Any("ids", xids))
219			return xids, nil
220			}
221
222			// getChanges is a method that retrieves the changes that occurred in the relation tuples within a specified transaction.
223			//
224			// ctx: The context.Context instance for managing the life-cycle of this function.
225			// value: The ID of the transaction for which to retrieve the changes.
226			// tenantID: The ID of the tenant for which to retrieve the changes.
227			//
228			// This method returns a TupleChanges instance that encapsulates the changes in the relation tuples within the specified
229			// transaction, or an error if something went wrong during execution.
230			func (w Watch) getChanges(ctx context.Context, value types.XID8, tenantID string) (base.DataChanges, error) {
231			// Initialize a new TupleChanges instance.
232			changes := &base.DataChanges{}
233
234			slog.DebugContext(ctx, "retrieving changes for transaction", slog.Any("id", value), slog.Any("tenant_id", tenantID))
235
236			// Construct the SQL SELECT statement for retrieving the changes from the RelationTuplesTable.
237			tbuilder := w.database.Builder.Select("entity_type, entity_id, relation, subject_type, subject_id, subject_relation, expired_tx_id").
238			From(RelationTuplesTable).
239			Where(squirrel.Eq{"tenant_id": tenantID}).Where(squirrel.Or{
240			squirrel.Eq{"created_tx_id": value},
241			squirrel.Eq{"expired_tx_id": value},
242			})
243
244			// Generate the SQL query and arguments.
245			tquery, targs, err := tbuilder.ToSql()
246			if err != nil {
247			slog.ErrorContext(ctx, "error while building sql query for relation tuples", slog.Any("error", err))
248			return nil, err
249			}
250
251			slog.DebugContext(ctx, "executing sql query for relation tuples", slog.Any("query", tquery), slog.Any("arguments", targs))
252
253			// Execute the SQL query and retrieve the result rows.
254			var trows pgx.Rows
255			trows, err = w.database.ReadPool.Query(ctx, tquery, targs...)
256			if err != nil {
257			slog.ErrorContext(ctx, "failed to execute sql query for relation tuples", slog.Any("error", err))
258			return nil, errors.New(base.ErrorCode_ERROR_CODE_EXECUTION.String())
259			}
260			// Ensure the rows are closed after processing.
261			defer trows.Close()
262
263			abuilder := w.database.Builder.Select("entity_type, entity_id, attribute, value, expired_tx_id").
264			From(AttributesTable).
265			Where(squirrel.Eq{"tenant_id": tenantID}).Where(squirrel.Or{
266			squirrel.Eq{"created_tx_id": value},
267			squirrel.Eq{"expired_tx_id": value},
268			})
269
270			aquery, aargs, err := abuilder.ToSql()
271			if err != nil {
272			slog.ErrorContext(ctx, "error while building SQL query for attributes", slog.Any("error", err))
273			return nil, err
274			}
275
276			slog.DebugContext(ctx, "executing sql query for attributes", slog.Any("query", aquery), slog.Any("arguments", aargs))
277
278			var arows pgx.Rows
279			arows, err = w.database.ReadPool.Query(ctx, aquery, aargs...)
280			if err != nil {
281			slog.ErrorContext(ctx, "error while executing SQL query for attributes", slog.Any("error", err))
282			return nil, errors.New(base.ErrorCode_ERROR_CODE_EXECUTION.String())
283			}
284			// Ensure the rows are closed after processing.
285			defer arows.Close()
286
287			// Set the snapshot token for the changes.
288			changes.SnapToken = snapshot.Token{Value: value}.Encode().String()
289
290			// Iterate through the result rows.
291			for trows.Next() {
292			var expiredXID types.XID8
293
294			rt := storage.RelationTuple{}
295			// Scan the result row into a RelationTuple instance.
296			err = trows.Scan(&rt.EntityType, &rt.EntityID, &rt.Relation, &rt.SubjectType, &rt.SubjectID, &rt.SubjectRelation, &expiredXID)
297			if err != nil {
298			slog.ErrorContext(ctx, "error while scanning row for relation tuples", slog.Any("error", err))
299			return nil, err
300			}
301
302			// Determine the operation type based on the expired transaction ID.
303			op := base.DataChange_OPERATION_CREATE
304			if expiredXID.Uint == value.Uint {
305			op = base.DataChange_OPERATION_DELETE
306			}
307
308			// Append the change to the list of changes.
309			changes.DataChanges = append(changes.DataChanges, &base.DataChange{
310			Operation: op,
311			Type: &base.DataChange_Tuple{
312			Tuple: rt.ToTuple(),
313			},
314			})
315			}
316
317			// Iterate through the result rows.
318			for arows.Next() {
319			var expiredXID types.XID8
320
321			rt := storage.Attribute{}
322
323			var valueStr string
324
325			// Scan the result row into a RelationTuple instance.
326			err = arows.Scan(&rt.EntityType, &rt.EntityID, &rt.Attribute, &valueStr, &expiredXID)
327			if err != nil {
328			slog.ErrorContext(ctx, "error while scanning row for attributes", slog.Any("error", err))
329			return nil, err
330			}
331
332			// Unmarshal the JSON data from `valueStr` into `rt.Value`.
333			rt.Value = &anypb.Any{}
334			unmarshaler := &jsonpb.Unmarshaler{}
335			err = unmarshaler.Unmarshal(strings.NewReader(valueStr), rt.Value)
336			if err != nil {
337			slog.ErrorContext(ctx, "failed to unmarshal attribute value", slog.Any("error", err))
338			return nil, err
339			}
340
341			// Determine the operation type based on the expired transaction ID.
342			op := base.DataChange_OPERATION_CREATE
343			if expiredXID.Uint == value.Uint {
344			op = base.DataChange_OPERATION_DELETE
345			}
346
347			// Append the change to the list of changes.
348			changes.DataChanges = append(changes.DataChanges, &base.DataChange{
349			Operation: op,
350			Type: &base.DataChange_Attribute{
351			Attribute: rt.ToAttribute(),
352			},
353			})
354			}
355
356			slog.DebugContext(ctx, "successfully retrieved changes for transaction", slog.Any("id", value))
357
358			// Return the changes and no error.
359			return changes, nil
360			}
361

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postgres.*Watch.getChanges D

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