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Questions tagged [mapping]

A type in solidity that allows access to arbitrary elements via a key, similar to a dictionary or hashmap in other languages.

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Best way to support restoring of all the keys of a mapping

I have a contract, in which I maintain the keys of a mapping in two different ways: Storing each key in an array Emitting an event for each key I do this in order to be able to restore the keys (and ...
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25 views

Default getter and setter for mapping in solidity

In my smart contract I've public mapping as mapping (uint=>User) public users where User is a Struct, so is there any way to get the values of this mapping using default getter. For Example : If ...
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24 views

Mapping or indexed event

I want to store data on chain that is not needed within a smart contract but should be retrieved easily and particularly quickly from outside. I know that storing the data within an indexed event is ...
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69 views

how do I loop through a mapping of address [duplicate]

I have a mapping of list of struct (mapping (address => struct[])) I'm having a trouble in how to display all them together in the front end (i'm using React js). Thnx.
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Use Values Returned from One Function in Another

need a little help if you can spare the time. Making a little card game where people can collect "warrior" cards. We'll have an initial 12 master "cards" that supply the initial traits for the ...
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1answer
34 views

In Ethereum how to check if in mapping, the key already exists?

In this Proof of existence, integrity, and ownership contract of a file why files[fileHash].timestamp == 0 is used? why timestamp? contract Proof { struct FileDetails { uint timestamp; ...
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42 views

How to search through blockchain?

I m doing project for document verification using blockchain in which we don't have to carry documents everywhere, hash key of block will fetch data of doc from blockchain.I m not getting how to ...
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2answers
52 views

access mapping inside mapping of struct in Solidity ^0.5.0

I have a contract which looks like this: contract a { struct Str { uint256 totalTokens; mapping(address => uint256) playerTokens; } mapping(uint256 => Str) public ...
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1answer
28 views

How Ethereum stores its data in the blockchain [duplicate]

I am new to ethereum and the blockchain, but I am wondering about blockchain databases. Mainly I am wondering how exactly the database data and the blockchain merge. For instance, in a database you ...
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1answer
17 views

Associate event struct to user addresses

I have two contracts. One called User and other called Event pragma solidity ^0.4.24; contract User { mapping(uint=>address) addresses; uint addressRegistryCount; } pragma solidity ^...
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1answer
83 views

Return a mapping in a getAll function

pragma solidity ^0.4.24; contract User { mapping(uint=>address) addresses; uint addressRegistryCount; function set(address userAddress) public { addresses[...
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1answer
12 views

How do I get product/parcelID from particular Assigned address using struct and mapping?

struct Sellers{ address sellerAddress; uint parcelId; uint parcelPrice; } In this struct I've entered multiple parcel Ids to sellerAddress and I've retreived them using _sellerAddress. ...
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Struct and Mapping input value error of Invalid Opcode while calling setSeller() to store multiple seller's addresses

What dose the -1 means? Or why we should use -1 while pushing one element in array. What should I enter in sellerAccounts: field as input? pragma solidity ^0.5.1; contract Seller{ struct ...
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Return an array of adresses

I have a mapping with the key as an address and the value as an array of addresses. How do I return the array of addresses? In older solidity versions it works. In newer compiler versions I have to ...
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2answers
100 views

Pure functions as a replacement of constant mappings?

I need to create a lookup table [uint -> uint] that is constant. Constant mappings or switch-case are not available in solidity. Are pure functions full of if-else the only option? Any better ...
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34 views

Why was mapping introduced in Solidity instead of a dictionary or map data strcuture?

What was the thought process behind introducing mapping in Solidity? Doesn't dictionary and map serve the same purpose in other languages? I want to know the necessity that led to the inclusion of ...
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1answer
38 views

How to access nested struct values?

I'm new in solidity programming so for learning purpose I'm developing e-voting system using ethereum blockchain. Code mentioned below, pragma solidity 0.4.25; contract RegisterCandidate { // ...
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39 views

Which is the expected behavior trying to get an undefined mapping value?

In ERC20 standard, _allowed is defined as: mapping (address => mapping (address => uint256)) private _allowed; and the getter function is defined as: function allowance(address owner, address ...
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2answers
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How do I read an array inside of a struct?

as part of learning solidity and smart-contract development, I am developing a simple part management/tracking system. I have a struct and a mapping for a list of parts as such: struct Part { uint ...
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Possible ERC-20 improvement: Token-specific ENS equivalent

With ENS still providing quite a difficult user experience for the average user, I'm wondering why standards like ERC-20 don't implement a simple mapping allowing people to set names equivalent to ...
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3answers
33 views

Is There any way to check if the entered key is having a corresponding value in a mapping or not?

Suppose In a banking system many people are enrolled (managed through mapping ) mapping (address => bool) enrolled; And only those can deposit who are enrolled in the bank. Can I check if ...
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1answer
49 views

How to initialize a new struct with an empty mapping? [duplicate]

For expl. mapping(uint => Test) tests; struct Test { uint id; mapping(address => uint) votes; } function newTest() public { test[0] = Test(0, <EMPTY_MAPPING>) }
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41 views

Return an array of mappings reflecting global state between struct associations?

I am looking for a construct that's something like "return an list of key value pairs," which I think would be implemented as an array of mappings. Is that right? That is, I'd like a data structure ...
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39 views

Is there a form of mapping with an even larger space?

I understand from here that the space for mapping() is drawn from a size of 2^256 * 32 bytes storage, which provides a 1 chance in 10^69 of overwrites. If I'm working with contracts on the order of ...
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Membership in a set of strings

I'm looking solidity help in storing a set of strings and checking for membership in that set. I have a concrete and an abstract question on that: Concrete What is the data structure in solidity ...
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2answers
134 views

How to delete or remove a key from mapping?

I have the following map: mapping (string => Category) categoryMap; Let's say the key was mistyped, so I want to remove the key and add a correct one, how would I do that? Function would be ...
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1answer
26 views

How to initialise a mapping of a struct inside a function?

Mappings are normally declared in the top part of the contract, however is there any way to instantiate a mapping - which belongs to a struct - while in a function?
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3answers
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How do I check if a bytes32 variable in a mapping has been assigned value?

For example, for: mapping(address => bytes32) public addressName; which one of the following syntax is correct? address _address = 0x...; //an actual address require(addressName[_address]!=""); ...
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16 views

Should I maintain an array of all the valid keys in a given mapping?

I have a contract which maintains a map of valid wallets. In this map, the keys are wallet addresses and the values are wallet parameters: struct WalletParams { bool valid; uint x; uint ...
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web3js send transaction failed when contract modify mapping data , but remix work

first, web3 version: 1.0.0-beta.36 the contract code is: pragma solidity ^0.4.25; contract Main { struct Model { uint256 key; uint64 createTime; } Model[] public models; mapping(...
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1answer
60 views

Mapping address to multidimensional uint

I'm trying to create an array contains addresses which belongs to particular transaction ID. Array structure: transactions[0x12345][0] = 123456 transactions[0x12345][1] = 789101 transactions[0x12345]...
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2answers
243 views

TypeError: Cannot read property 'call' of undefined

I am trying to read a mapping inside my smart contract that looks like this: mapping(address => User) public users; My web3js code looks like this. I am trying to read mapping users inside the ...
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1answer
61 views

Getting and storing address of erc20 contract after dynamically creating it

I have a function which dynamically creates an ERC20 contract on calling a function in another contract as follows: function createDao(string _tokenName) public payable { tokenNumberIndex = ...
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1answer
37 views

pagination when reading mappings in solidity

I am trying to read a lot of data from a smart contract mapping, How can I include pagination when retrieving data through smart contract methods?
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1answer
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Do I need to delete mappings that I don't need anymore?

I have a struct like this: struct Game { string gameID; string[2] teams; string winningTeam; string losingTeam; mapping(string => uint) totalWeiBet; ...
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1answer
1k views

How to loop through a array of addresses?

I have a mapping and an array that contains a list of addresses of students. When I loop over that array, the method .length is not working. How can I loop through the array Student_list shown below?...
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3answers
321 views

How to map an address with a string array in solidity?

Goal: I wish to store an array of names with an address in a smart contract. It's more like Key-Value pairs where addresses are paired with a list of type strings. Can I use mapping to implement this?...
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1answer
45 views

How to dynamicaly edit a mapping

I want to be able to edit values in a struct. My struct is declared and mapped like this : struct entityLinks{ string linksUrl; string linksName; } mapping (uint => ...
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1answer
17 views

Gas used for the same deterministic operation is different

standard ICO function which exchanges Ether to ERC20 token balance. Call 1, used 49431: https://ropsten.etherscan.io/tx/0x6671c8fd39d195b09868d914d80f0e884e42259c7346b69afb483f2e18fae263 Call 2, ...
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1answer
75 views

Sorting elements from mapping according to certain value?

I have created a function that receive some values from users an store them in a mapping. How to arrange the stored values in mapping according to a certain value ( Priority as in the shown example ...
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3answers
60 views

Smart Contracts Mappings

I am trying to understand smart contracts mappings. Imagine I have smart contract that can create an object "car" and store in its mapping. This object has parameter like "tires" with black value. ...
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1answer
95 views

Updating a field in structure - One to many mapping - Solidity

I have a structure Student with one to many mapping and pushed values to it.Following is my code: pragma solidity ^0.4.20; struct Student{ uint id; string name; uint256 mark; } mapping(...
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2answers
131 views

Why use arrays and not mappings? [duplicate]

So I was implementing a trading contract and need to keep a list of products on sale. I was using arrays but later switched to mappings. So arrays implementation: uint[] public productsOnSale; uint ...
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1answer
95 views

Changing dynamic array index content

I'm trying to to make a contract which lets the user choose any number he likes to populate an array of integers used in a mapping. Then he can choose any index of this array to increase its value by ...
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2answers
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How to maintain history of changes in mapping?

I have a mapping variable in my solidity code which maps address to name. I want to maintain the history/log of every change that happens in this mapping. What is the best possible solution to it?
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1answer
27 views

Array of items vs mapping+array of ids with web3js?

In most articles they recommend to use mapping. But mappings don't allow to iterate their items directly. And nobody says what to do if you need to get all the stored items. In my case I need store ...
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1answer
53 views

Can i create a new address this way?

I am busy with a project. So I have an array of a struct within another struct. In this case for example array of CattleHealth in Cattle. In my RecordHealth function, I am taking the address of the ...
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1answer
33 views

How to add an instance of a struct to an array of another?

Hi I am pretty new to solidity. I am busy with a project that records all kinds of information about cattle. In my code below my cattle struct has an array of CattleHealth and CattleGrowth which are ...
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1answer
154 views

How to map Array of Structs in Solidity [duplicate]

Need this architecture { address1 => [struct1, struct2], address2 => [struct1, struct2, struct3,], address3 => [struct1, struct2, struct3, struct4, struct5], ......
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91 views

Array of Struct always returns 0x0 at index 0

Here's my sample contract code. contract SimpleStore { uint public BetRound; uint public SelectedUser; struct Struct { uint _round; address _owner; uint _index; bool _active; ...