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How to use python in ultisnips
This snippet uses python to convert camel case to underline. It is an example to use python in ultisnips. t[1] gets content of $1. After the convert, assign the result to snip.rv.
snippet gfk "gorm foreign key"
$1ID uint \`gorm:"column:`!p name=re.sub(r"(\w)([A-Z])", r"\1_\2", t[1]).lower(); snip.rv = name`_id" json:"-"\`
${1:Model} $1 \`gorm:"foreignKey:$1ID" json:"`!p name=re.sub(r"(\w)([A-Z])", r"\1_\2", t[1]).lower(); snip.rv = name`"\`
endsnippet