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database/sqlでNullを扱う歴史とsql.Null[T]の登場 / sql.Nul...
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mackee
May 17, 2024
Programming
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830
database/sqlでNullを扱う歴史とsql.Null[T]の登場 / sql.Null[T] history
kamakura.go #6
https://kamakurago.connpass.com/event/316438/
mackee
May 17, 2024
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Transcript
database/sqlͰNULLΛѻ͏ ྺ࢙ͱsql.Null[T]ͷొ kamakura.go #6 @mackee_w a.k.a macopy 2024-05-17
Δਓ • X: @mackee_w • GitHub: @mackee • ໘ന๏ਓΧϠοΫ •
Tonamel αʔόʔαΠυΤϯδχΞ
database/sqlͰNULLΛѻ͏ ͱʁ
database/sqlͰNULLΛѻ͏
database/sqlͰNULLΛѻ͏ • sql.Null**ͱ͍͏ܕͰϥοϓͯ͠ग़͠ೖΕΛ͢Δ • ϙΠϯλܕͰͳ͍(͕ɺϙΠϯλܕͷnilΛαϙʔτ͍ͯ͠Δέʔε͋Δ) • sql.Null**Validͱ͍͏ϑΟʔϧυ͕͋Δ • Valid͕falseͩͱNull, trueͩͱNullͰͳ͍
• ValidͱผʹΛ֨ೲ͢ΔϑΟʔϧυ͕͋Δ • sql.NullStringͰ͋Ε `String string`, sql.NullInt64Ͱ͋Ε`Int64 int64`
ͦͦdatabase/sqlͰѻ͏ͬͯͳΜͩʁ • جຊతʹҎԼͷinterface͕࣮͞Ε͍ͯΔܕ • SQLͷͱͯ͠͏߹ database/sql/driver.Valuer • ΫΤϦͷ݁Ռ͔Βड͚औͬͨͷΛGoͷมʹόΠϯυ͢Δ߹ɺ database/sql.Scanner •
GoͷϓϦϛςΟϒܕdriverྀ͕͍ͯ͠Δܕͦͷ··ಥͬࠐΊΔ • ޙऀͷྫ: json.RawMessage(go-sql-driver/mysql)
driver.ValuerͰNULLΛSQLʹೖΕΔʹ • driver.Valuer.Value()͕nilΛฦͤྑ͍ • sql.Null**ͳͲͦ͏ͳ͍ͬͯΔ • driver.Valuer.Value()͕typed-nilΛฦͨ͠߹ʁ • driver͘͠database/sql/driverͰuntyped-nilʹม͞Ε͍ͯΔ ͷͰηʔϑ
• Ͱuntyped-nilΛฦͨ͠ํ͕(͓ߦّ)ྑ͍Ͱ͢Ͷ
driver.ScanͰNULLΛड͚Δʹʁ • driver.Scanner.Scanʹuntyped-nil͕ೖͬͯ͘ΔͷͰɺͦΕͰValidͷ ఆΛߦ͏ • sql.Null**ʹnil͕ೖͬͨ߹Validʹfalse͕ೖΓɺ͕ೖΔ fi eldʹθ ϩ͕ೖΔΑ͏ʹͳ͍ͬͯΔ •
driver.ScannerͰͳ͘ϙΠϯλܕͰnullΛड͚ͨΒnil͕ೖΔ • Ͱθϩnilͱݟ͚͕͔ͭͳ͍͔ʁ ؾ͕͢Δ͚ͩͳͷͰ۩ମతͳ έʔε͕͋ͬͨΒڭ͍͑ͯͩ͘͞
database/sqlʹ͓͚Δsql.Null**ͷྺ࢙ • sql.NullStringdatabase/sqlύοέʔδ͕࡞ΒΕͨ࣌Ͱଘࡏ͢Δ(2011/09/29) • ࣌sql.NullableStringͱ͍͏໊લͰScannerInfo interface͕࣮͞Ε͍ͯͨ • sql.NullInt64, sql.NullFloat64, sql.BoolՃ(2012/01/26)
• ͜ͷޙgo1͕ϦϦʔε • sql.NullTimeՃ(2019/04/06), sql.NullInt32Ճ(2019/04/27), sql.NullInt16, sql.NullBytesՃ(2021/05/05)
Β͘sql.NullTime͕ͳ͔ͬͨ • ͳ͔ͬͨͷͰgo-sql-driver/mysql.NullTimeΛ͍ͬͯͨਓ͍ͨͰ ͠ΐ͏(2013/04/26͔Βଘࡏ) • ͦͷଞsql.Null**(͜͜ʹҙͷܕ͕ೖΔ)͕ཉ͍͠ํ͍ͬͺ͍͍ͨͰ ͠ΐ͏ • ϥΠϒϥϦͳΓࣗલ࣮ͳΓ͕ඞཁͰ͋ͬͨ… •
ͦΕͦΕͰϓϩδΣΫτ͝ͱʹҧ͏ͱ͍͏ࠞཚͷͱʹ…
from Go1.22 Release Notes The new Null[T] type provide a
way to scan nullable columns for any column types.
sql.Null[T]ͱ • sql.Null[T(͜͜ʹҙͷܕ͕ೖΔ)]ͷΑ͏ʹ༻͢Δ͜ͱͰɺsql.Null**ͱಉ͡ޮ ྗΛ࣋ͭܕ • sql.Null**Λ૿͞ͳͯ͘ྑ͘ͳͬͨʂ • user de fi
ned typeͱͷΈ߹Θ͕ͤྑ͍ • type HogeID uint64 ͷΑ͏ͳIDܕ࡞ͬͨ߹ʹɺͦͷNullableͳܕͱͯ͠ `sql.Null[HogeID]`͕͑Δ • methane͞ΜฒͼʹGoνʔϜͷօ͞Μ͋Γ͕ͱ͏ʂ
FAQ • Q: ࣮࣭Option/MaybeܕͰʁ • A: IssueʹͦΜͳ͕ٞ͋Γ·͕ͨ͠ɺSQLΛॻ͘ͱ͖ɺDB͔Βͷ ΫΤϦ݁ՌΛಡΉ࣌ʹͷΈ͍·͠ΐ͏Ͷ • Q:
͜Ε͕ೖͬͨܦҢʁ • A: ͱͱsql.NullUInt64ͷఏҊ͕͞Εͨ࣌ʹʮδΣωϦΫεΛͬ ͯͶʯͱ͍͏ʹͳ͍ͬͯͨ
Ҏ্ʂ