Inventories, net of inventory reserves - Summary of Movement of Inventory Provision (Detail) - CNY (¥) ¥ in Thousands	12 Months Ended
Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Inventory Disclosure [Abstract]
At beginning of year	¥ 266	¥ 273	¥ 527
Provision/(reversal)	311	(7)	(254)
At end of year	¥ 577	¥ 266	¥ 273

Amount of inventory reserves for last-in first-out (LIFO) and other inventory valuation methods.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=116847112&loc=d3e4492-108314

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant