how to modify the stored data in a block chain?

Question

I am trying to implement a blockchain using python. and I have a block like below

{
    studentId:100,
    marks:200
}

I just want to update this marks to 300. so can i do this in a block chain. I heard that we couldn't update a bockchain

Just recalculate the block and everything after it. – Ignacio Vazquez-Abrams Feb 18 '18 at 05:19 — Ignacio Vazquez-Abrams, Feb 18 '18 at 05:19

score 0 · Accepted Answer · answered Feb 18 '18 at 05:34

0

One of the foundations of a blockchain is that the data in the blocks, once written, are immutable. The only way to "change" blockchain data is to add data to a new block that states that there has been a change. So instead of code that modifies an existing block to change marks from 200 to 300, you need to add a new point of data that states that student 100 has marks that are equal to 300.

answered Feb 18 '18 at 05:34

Yserbius

1,375
12
18

Thank you Yserbius. My doubts is , I always store the above data to a variable called "studentMarks". so get the student's latest mark , should i take the last block always . Right? also If i want to reduce 100 marks from 300 . I must create anew block and save it to "studentMarks". Right – learner Feb 18 '18 at 08:18
Sounds about right. Are you following a tutorial? What is uour code based on? – Yserbius Feb 18 '18 at 17:53

how to modify the stored data in a block chain?

1 Answers1