How to Safely Store uint64 Values in PostgreSQL\'s int64 Field?

Converting uint64 to int64 for PostgreSQL Storage

To handle the storage of a uint64 value in PostgreSQL, which only supports signed 64-bit integers (BIGINT), a simple type conversion is most effective. This approach preserves the binary representation of the uint64 value while casting it to int64.

Consider the following Go code:

import (
  "fmt"
)

func main() {
  i := uint64(0xffffffffffffffff) // Example uint64 value

  // Cast the uint64 to int64 using a type conversion
  i2 := int64(i)

  fmt.Println(i, i2)
}

This code outputs:

18446744073709551615 -1

As you can see, the type conversion of the uint64 value (18446744073709551615) to an int64 value (-1) is a success. This is because numeric conversion between uint64 and int64 doesn't alter the memory representation but only the type interpretation.

However, a caveat to note is that if you attempt to convert an untyped integer constant that exceeds the int64 value range, a compile-time error will occur. For example:

i3 := int64(0xffffffffffffffff) // Compile time error!

This error occurs because the constant value 0xffffffffffffffff overflows the int64 value range (0x7fffffffffffffff).

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