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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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Can I init mapping in solidity with pre-defined values?

f.e in Python: mappingName = { 'key1': 'value1', 'key2': 'value2' } What are the best practices to achieve that?
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How can I push data to array when using mapping (address => address[]) mappingName?

What is the exact syntax to push data using the above given syntax?
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What is the maximum storage size to store number of addresses in array? [duplicate]

I want to map multiple addresses using one address by doing this: mapping (address => arrayOfAddresses[]) mappingName; What is the maximum size of addresses I can store in that array?
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24 views

map multikey how-to?

I'm trying to create a map whose key is composed of two bytes32 keys. I've tried with tuples-keys and struct-keys but both are rejected by the compiler. I'm also thinking about "hashing" both keys ...
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Problem on returning fields of a struct inside a mapping

I have the above code mapping(string => Owner) public Owners; function addOwner( string memory name, string memory surname, string memory fathername, string memory mothername, string memory ...
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46 views

DeclarationError: identifier not found or not unique 'candidate'

I got the above error at the mapping 'candidate' pragma solidity ^0.4.22; contract Election { struct Candidates { string name; uint voteCount; } struct voter { bool authorized; ...
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54 views

Reset all values in a mapping

I am trying to figure out how to have the balance of all players reset to (amount) when a certain condition happens. This is the function that will update a specific player balance. How do I make it ...
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27 views

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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87 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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26 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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3answers
169 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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15 views

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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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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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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119 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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29 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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28 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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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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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
120 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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38 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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63 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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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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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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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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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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40 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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1answer
21 views

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
216 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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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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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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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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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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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
76 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
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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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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
392 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
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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
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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
100 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
72 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
133 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
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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 ...