I am trying to code a smart contract and I am using a mapping (address => bool) ; i make it true when a certain conditions meet. Now for another condition I want my mapping to reset and loose all of its data , i want it to be where it was in the beginning a empty mapping.
CODE IMAGE
Problem statement : I am setting all true for whoever voted using in my Dapp using a mapping ( address => bool ) now after voting is ended i want all my mapping values to be false , is there any efficient way to solve this
Thank you in advance..
Now for another condition I want my mapping to reset and loose all of its data , i want it to be where it was in the beginning a empty mapping.
The only way to reset mapping is to iterate through all the keys and set values to zero. This is not practical in Solidity.
Instead, you probably want to use mapping with the third layer and having data tuple of (version, key, value). Then just increment version when you want to do a full reset.
Alternatively you can do (key, version, value) and compare the version every time the key is read. This approach could be more gas efficient, as you are using the same storage lot when rewriting values.
I have found this as most feasible so far;
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.6.0 <0.9.0;
contract Map {
mapping (uint => uint)[] array;
function allocate(uint newMaps) public {
for (uint i = 0; i < newMaps; i++)
array.push();
}
function writeMap(uint map, uint key, uint value) public {
array[map][key] = value;
}
function readMap(uint map, uint key) public view returns (uint) {
return array[map][key];
}
function eraseMaps() public {
delete array;
}
}
Related
I am trying to create a custom collector in order to count valid elements of a list. I have done it using one of the already provide collectors:
arr.stream()
.filter(e -> e.matches("[:;][~-]?[)D]"))
.map(e -> 1)
.reduce(0, Integer::sum);
but as a challenge for myself, I wanted to create my own custom collector in order to understand it better. And this is where I got stuck.
It is probably something trivial but I am learning this and can't figure a supplier, an accumulator, and a combiner. I guess I still don't understand something about them. For instance, I have a similar stream:
arr1.stream()
.filter(e -> e.matches("[:;][~-]?[)D]"))
.map(e -> 1)
.collect(temporary array, adding to array, reduce);
AFAIK supplier is a function without arguments, which returns something. I studied standard examples and it is usually a method reference for a new collection, e.g. ArrayList::new. I tried to use constant 0, e -> 0 because I want to return a scalar. I think it is wrong because it makes the stream returning 0. If using method reference for a temporary collection, Java complains about a mismatch of types of a supplier and returning object. I am also confused about using an accumulator if the final result is a number as a combiner would reduce all elements to a number, e.g. (a,b) -> a + b`.
I'm completely stumped.
Probably part of your problem is that you cannot obviously create an accumulator for an Integer type since it is immutable.
You start with this:
System.out.println(IntStream.of(1,2,3).reduce(0, Integer::sum));
You can extend to this:
System.out.println(IntStream.of(1,2,3).boxed()
.collect(Collectors.reducing(0, (i1,i2)->i1+i2)));
Or even this, which has an intermediate mapping function
System.out.println(IntStream.of(1,2,3).boxed()
.collect(Collectors.reducing(0, i->i*2, (i1,i2)->i1+i2)));
You can get this far with your own Collector
Collector<Integer, Integer, Integer> myctry = Collector.of(
()->0,
(i1,i2)->{
// what to do here?
},
(i1,i2)->{
return i1+i2;
}
);
The accumulator is A function that folds a value into a mutable result container with mutable being the keyword here.
So, make a mutable integer
public class MutableInteger {
private int value;
public MutableInteger(int value) {
this.value = value;
}
public void set(int value) {
this.value = value;
}
public int intValue() {
return value;
}
}
And now:
Collector<MutableInteger, MutableInteger, MutableInteger> myc = Collector.of(
()->new MutableInteger(0),
(i1,i2)->{
i1.set(i1.intValue()+i2.intValue());
},
(i1,i2)->{
i1.set(i1.intValue()+i2.intValue());
return i1;
}
);
And then:
System.out.println(IntStream.of(1,2,3)
.mapToObj(MutableInteger::new)
.collect(myc).intValue());
Reference:
Example of stream reduction with distinct combiner and accumulator
EDIT: The finisher just does whatever with the final result. If you don't set it on purpose then it is set by default to IDENTITY_FINISH which is Function.identity() which says just to return the final result as is.
EDIT: If you're really desperate:
Collector<int[], int[], int[]> mycai = Collector.of(
()->new int[1],
(i1,i2)->i1[0] += i2[0],
(i1,i2)->{i1[0] += i2[0]; return i1;}
);
System.out.println(IntStream.of(1,2,3)
.mapToObj(v->{
int[] i = new int[1];
i[0] = v;
return i;
})
.collect(mycai)[0]);
I am using BeanItemContainer for my Grid. I want to get a unique list of one of the properties. For instance, let's say my beans are as follows:
class Fun {
String game;
String rules;
String winner;
}
This would display as 3 columns in my Grid. I want to get a list of all the unique values for the game property. How would I do this? I have the same property id in multiple different bean classes, so it would be nice to get the values directly from the BeanItemContainer. I am trying to avoid building this unique list before loading the data into the Grid, since doing it that way would require me to handle it on a case by case basis.
My ultimate goal is to create a dropdown in a filter based on those unique values.
There isn't any helper for directly doing what you ask for. Instead, you'd have to do it "manually" by iterating through all items and collecting the property values to a Set which would then at the end contain all unique values.
Alternatively, if the data originates from a database, then you could maybe retrieve the unique values from there by using e.g. the DISTINCT keyword in SQL.
In case anyone is curious, this is how I applied Leif's suggestion. When they enter the dropdown, I cycle through all the item ids for the property id of the column I care about, and then fill values based on that property id. Since the same Grid can be loaded with new data, I also have to "clear" this list of item ids.
filterField.addFocusListener(focus->{
if(!(filterField.getItemIds() instanceof Collection) ||
filterField.getItemIds().isEmpty())
{
BeanItemContainer<T> container = getGridContainer();
if( container instanceof BeanItemContainer && getFilterPropertyId() instanceof Object )
{
List<T> itemIds = container.getItemIds();
Set<String> distinctValues = new HashSet<String>();
for(T itemId : itemIds)
{
Property<?> prop = container.getContainerProperty(itemId, getFilterPropertyId());
String value = null;
if( prop.getValue() instanceof String )
{
value = (String) prop.getValue();
}
if(value instanceof String && !value.trim().isEmpty())
distinctValues.add(value);
}
filterField.addItems(distinctValues);
}
}
});
Minor point: the filterField variable is using the ComboBoxMultiselect add-on for Vaadin 7. Hopefully, when I finally have time to convert to Vaadin 14+, I can do something similar there.
I Use this sample for search in Map but not work :|:
var xmenList = ['4','xmen','4xmen','test'];
var xmenObj = {
'first': '4',
'second': 'xmen',
'fifth': '4xmen',
'author': 'test'
};
print(xmenList.indexOf('4xmen')); // 2
print(xmenObj.indexOf('4xmen')); // ?
but I have error TypeError: xmenObj.indexOf$1 is not a function on last code line.
Pelease help me to search in map object simple way same as indexOf.
I found the answer:
print(xmenObj.values.toList().indexOf('4xmen')); // 2
or this:
var ind = xmenObj.values.toList().indexOf('4xmen') ;
print(xmenObj.keys.toList()[ind]); // fifth
Maps are not indexable by integers, so there is no operation corresponding to indexOf. If you see lists as specialized maps where the keys are always consecutive integers, then the corresponding operation should find the key for a given value.
Maps are not built for that, so iterating through all the keys and values is the only way to get that result.
I'd do that as:
K keyForValue<K, V>(Map<K, V> map, V value) {
for (var entry in map.entries) {
if (entry.value == value) return key;
}
return null;
}
The entries getter is introduced in Dart 2. If you don't have that, then using the map.values.toList().indexOf(value) to get the iteration position, and then map.keys.elementAt(thatIndex) to get the corresponding key.
If you really only want the numerical index, then you can skip that last step.
It's not amazingly efficient (you allocate a new list and copy all the values). Another approach is:
int indexOfValue<V>(Map<Object, V> map, V value) {
int i = 0;
for (var mapValue in map.values) {
if (mapValue == value) return i;
i++;
}
return -1;
}
You can search using .where(...) if you want to find all that match or firstWhere if you assume there can only be one or you only want the first
var found = xmenObj.keys.firstWhere(
(k) => xmenObj[k] == '4xmen', orElse: () => null);
print(xmenObj[found]);
This query produces an error No value given for one or more required parameters:
using (var conn = new OleDbConnection("Provider=..."))
{
conn.Open();
var result = conn.Query(
"select code, name from mytable where id = ? order by name",
new { id = 1 });
}
If I change the query string to: ... where id = #id ..., I will get an error: Must declare the scalar variable "#id".
How do I construct the query string and how do I pass the parameter?
The following should work:
var result = conn.Query(
"select code, name from mytable where id = ?id? order by name",
new { id = 1 });
Important: see newer answer
In the current build, the answer to that would be "no", for two reasons:
the code attempts to filter unused parameters - and is currently removing all of them because it can't find anything like #id, :id or ?id in the sql
the code for adding values from types uses an arbitrary (well, ok: alphabetical) order for the parameters (because reflection does not make any guarantees about the order of members), making positional anonymous arguments unstable
The good news is that both of these are fixable
we can make the filtering behaviour conditional
we can detect the category of types that has a constructor that matches all the property names, and use the constructor argument positions to determine the synthetic order of the properties - anonymous types fall into this category
Making those changes to my local clone, the following now passes:
// see https://stackoverflow.com/q/18847510/23354
public void TestOleDbParameters()
{
using (var conn = new System.Data.OleDb.OleDbConnection(
Program.OleDbConnectionString))
{
var row = conn.Query("select Id = ?, Age = ?", new DynamicParameters(
new { foo = 12, bar = 23 } // these names DO NOT MATTER!!!
) { RemoveUnused = false } ).Single();
int age = row.Age;
int id = row.Id;
age.IsEqualTo(23);
id.IsEqualTo(12);
}
}
Note that I'm currently using DynamicParameters here to avoid adding even more overloads to Query / Query<T> - because this would need to be added to a considerable number of methods. Adding it to DynamicParameters solves it in one place.
I'm open to feedback before I push this - does that look usable to you?
Edit: with the addition of a funky smellsLikeOleDb (no, not a joke), we can now do this even more directly:
// see https://stackoverflow.com/q/18847510/23354
public void TestOleDbParameters()
{
using (var conn = new System.Data.OleDb.OleDbConnection(
Program.OleDbConnectionString))
{
var row = conn.Query("select Id = ?, Age = ?",
new { foo = 12, bar = 23 } // these names DO NOT MATTER!!!
).Single();
int age = row.Age;
int id = row.Id;
age.IsEqualTo(23);
id.IsEqualTo(12);
}
}
I've trialing use of Dapper within my software product which is using odbc connections (at the moment). However one day I intend to move away from odbc and use a different pattern for supporting different RDBMS products. However, my problem with solution implementation is 2 fold:
I want to write SQL code with parameters that conform to different back-ends, and so I want to be writing named parameters in my SQL now so that I don't have go back and re-do it later.
I don't want to rely on getting the order of my properties in line with my ?. This is bad. So my suggestion is to please add support for Named Parameters for odbc.
In the mean time I have hacked together a solution that allows me to do this with Dapper. Essentially I have a routine that replaces the named parameters with ? and also rebuilds the parameter object making sure the parameters are in the correct order.
However looking at the Dapper code, I can see that I've repeated some of what dapper is doing anyway, effectively it each parameter value is now visited once more than what would be necessary. This becomes more of an issue for bulk updates/inserts.
But at least it seems to work for me o.k...
I borrowed a bit of code from here to form part of my solution...
The ? for parameters was part of the solution for me, but it only works with integers, like ID. It still fails for strings because the parameter length isn't specifed.
OdbcException: ERROR [HY104] [Microsoft][ODBC Microsoft Access Driver]Invalid precision value
System.Data.Odbc. OdbcParameter.Bind(OdbcStatementHandle hstmt,
OdbcCommand command, short ordinal, CNativeBuffer parameterBuffer, bool allowReentrance)
System.Data.Odbc.OdbcParameterCollection.Bind(OdbcCommand command, CMDWrapper cmdWrapper, CNativeBuffer parameterBuffer)
System.Data.Odbc.OdbcCommand.ExecuteReaderObject(CommandBehavior behavior, string method, bool needReader, object[] methodArguments, SQL_API odbcApiMethod)
System.Data.Odbc.OdbcCommand.ExecuteReaderObject(CommandBehavior behavior, string method, bool needReader)
System.Data.Common.DbCommand.ExecuteDbDataReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken)
Dapper.SqlMapper.QueryAsync(IDbConnection cnn, Type effectiveType, CommandDefinition command) in SqlMapper.Async.cs
WebAPI.DataAccess.CustomerRepository.GetByState(string state) in Repository.cs
var result = await conn.QueryAsync(sQuery, new { State = state });
WebAPI.Controllers.CustomerController.GetByState(string state) in CustomerController .cs
return await _customerRepo.GetByState(state);
For Dapper to pass string parameters to ODBC I had to specify the length.
var result = await conn.QueryAsync<Customer>(sQuery, new { State = new DbString { Value = state, IsFixedLength = true, Length = 4} });
I have a listview that I fill from an Adapter. My original code the data was being returned from a table, but now I need to get the code from a query with a join so the examples I used will no longer work and I haven't been able to find out how to use a query for this. I'm using an ORMrepository.
In my ORMrepository I have this function
public IList<Coe> GetmyCoe()
{
using (var database = new SQLiteConnection(_helper.WritableDatabase.Path))
{
string query = "SELECT Coe.Id, Adult.LName + ', ' + Adult.MName AS Name, Coe.Createdt FROM Adult INNER JOIN Coe ON Adult.CoeMID = Coe.Id";
return database.Query<Coe>(query);
}
}
which actually returns the data I want.
then in my Activity page I have this.
_list = FindViewById<ListView>(Resource.Id.List);
FindViewById<ListView>(Resource.Id.List).ItemClick += new System.EventHandler<ItemEventArgs>(CoeList_ItemClick);
var Coe = ((OmsisMobileApplication)Application).OmsisRepository.GetmyCoe();
_list.Adapter = new CoeListAdapter(this, Coe);
My Adapter page is where I have the problem, I know it is set up to to looking at a table which I'm not doing anymore. But I don't know how to change it for what I'm passing into it now. Current CoeListAdapter is:
public class CoeListAdapter : BaseAdapter
{
private IEnumerable<Coe> _Coe;
private Activity _context;
public CoeListAdapter(Activity context, IEnumerable<Coe> Coe)
{
_context = context;
_Coe = Coe;
}
public override View GetView(int position, View convertView, ViewGroup parent)
{
var view = (convertView
?? _context.LayoutInflater.Inflate(
Resource.Layout.CoeListItem, parent, false)
) as LinearLayout;
var Coe = _Coe.ElementAt(position);
view.FindViewById<TextView>(Resource.Id.CoeMID).Text = Coe.Id.ToString();
//view.FindViewById<TextView>(Resource.Id.GrdnMaleName).Text = Coe.Name;
view.FindViewById<TextView>(Resource.Id.CreateDt).Text = Coe.CreateDt;
return view;
}
public override int Count
{
get { return _Coe.Count(); }
}
public Coe GetCoe(int position)
{
return _Coe.ElementAt(position);
}
public override Java.Lang.Object GetItem(int position)
{
return null;
}
public override long GetItemId(int position)
{
return position;
}
}
How do I set up the CoeListAdapter.cs page so that it can use the passed in data. As you can see I have a commented out lines where I fill a TextView which error because Coe.Name is not in the table model for Coe. but it is returned in the query. I believe my problem is IEnumerable but what do I change it to. I'm new to Mobile developement and suing VS2010 for Mono
The problem probably lies with the binding/mapping of the object not the creation of the view.
Or probably more specifically, the query.
Adult.LName + ', ' + Adult.MName AS Name
this should be:
Adult.LName || ', ' || Adult.MName AS Name
See also: String concatenation does not work in SQLite
From the sqlite docs: http://www.sqlite.org/lang_expr.html under the Operators heading:
The unary operator + is a no-op. It can be applied to strings,
numbers, blobs or NULL and it always returns a result with the same
value as the operand.
Note that there are two variations of the equals and not equals
operators. Equals can be either = or ==. The non-equals operator can
be either != or <>. The || operator is "concatenate" - it joins
together the two strings of its operands. The operator % outputs the
value of its left operand modulo its right operand.
The result of any binary operator is either a numeric value or NULL,
except for the || concatenation operator which always evaluates to
either NULL or a text value.
This shows that the + will evaluate to zero. If you use ||, the value will either be the correct value or NULL (if either of Adult.LName or Adult.MName is NULL).
This can be fixed by:
coalesce(first, '') || ', ' || coalesce(second, '')
but this may result in , LastName or FirstName,.
Another way would be to create another two properties in Coe called LName and MName.
Then bind the values to those properties and use the Name property like this:
public string Name
{
get { return string.Join(", ", LName, MName); }
}
This will probably be better as you can change how the Name appears especially if there are different combinations of First, Middle and Last names in different places.
And off topic:
I believe my problem is IEnumerable...
This is probably not too true as it returns the correct values. A better way would be to use IList as IEnumerable will iterate through the list each time to get the item as it does not know that the collection is actually a list. (I think)
thanks for the help on the concantination, I did find that was wrong, I did fix my problem, I was using an example by Greg Shackles on how to set up using a data base. what I had to do was create a new model with the elements I was wanting. So I created a new Model and called it CoeList, then everywhere I had List or IEnumerable I changed it to List or IEnumerable and it worked.