public StringExpression substring(int beginIndex, Expression<Integer> endIndex) {
        return Expressions.stringOperation(Ops.SUBSTR_2ARGS, mixin, ConstantImpl.create(beginIndex), endIndex);
    }
Create a {@code this.substring(beginIndex, endIndex)} expression

@param beginIndex inclusive start index
@param endIndex exclusive end index
@return this.substring(beginIndex, endIndex)
@see java.lang.String#substring(int, int)
querydsl-core/src/main/java/com/querydsl/core/types/dsl/StringExpression.java