Boolean isSuccess = true;
if(aMap.size() != bMap.size())
{
return false;
}
aMap.entrySet().forEach(entry -> {
AKey aKey = entry.getKey();
BValue bValue = bMap.get(aKey);
if(bValue == null)
return;
AValue aValue = entry.getValue();
if(!aValue.getClosed().equals(bValue.getClosed()))
return;
if(!aValue.getClosedToArrival().equals(bValue.getClosedToArrival()))
return;
if(!aValue.getClosedToDeparture().equals(bValue.getClosedToDeparture()))
return;
if(!aValue.getLengthOfStayArrival().equals(bValue.getLengthOfStayArrival()))
return;
});
return isSuccess;
How can i return false when validation failure?
i tried to add return false, such as below:
if(!aValue.getLengthOfStayArrival().equals(bValue.getLengthOfStayArrival()))
return false;
but it is unexpected expression, who can help me have a look?
You can't return false because you are in a lambda expression which implement the Consumer functional interface which method is of void type.
Instead, use anyMatch or noneMatch or allMatch :
return aMap.entrySet().stream().anyMatch(entry -> {
return false;// Put your condition here
});
I would also recommend to extract the validation in a method so that your pipeline looks like this :
return aMap.entrySet()
.stream()
.anyMatch(this::checkIfMatch);
Most of the times when opening {}, it's a good sign that you should create a new method.
Related
Hello I have a common function which looks like below,
public async Task<SPResponse> ExecuteAsync(string spName, DynamicParameters p)
{
SPResponse response = new SPResponse();
using (SqlConnection conn = new SqlConnection(_connStr))
{
conn.Open();
using (SqlTransaction transaction = conn.BeginTransaction(IsolationLevel.ReadCommitted))
{
try
{
p.Add("#SP_MESSAGE", dbType: DbType.String, direction: ParameterDirection.Output, size: 4000);
p.Add("#RETURNSTATUS", dbType: DbType.Int32, direction: ParameterDirection.ReturnValue);
await conn.ExecuteAsync(sql: spName, param: p, commandType: CommandType.StoredProcedure, transaction: transaction);
response.ReturnMessage = p.Get<string>("#SP_MESSAGE");
response.ReturnStatus = Convert.ToString(p.Get<int>("#RETURNSTATUS"));
if (response.ReturnStatus == "0")
{
response.Ref1 = Convert.ToString(p.Get<int>("#SP_ID"));
transaction.Commit();
}
else
{
transaction.Rollback();
}
}
catch (Exception ex)
{
Utils.Logger.Instance.LogException(ex);
transaction.Rollback();
}
conn.Close();
}
}
return response;
}
now on response.Ref1 = Convert.ToString(p.Get<int>("#SP_ID")); line in some of my procedure I am getting SP_ID as output parameter and in some I am not getting SP_ID as output parameter
but the problem is when I am not returning SP_ID as output parameter I am getting error of
The given key was not present in the dictionary.
I want to check the key before execution of p.get<int>()
how can I do this?
So I fixed this by myself and thanks to #MarcGravell.
I declared a parameter in my DapperClass where I am using common ExecuteAsync method.
private DynamicParameters _Param;
public DapperClass()
{
_Param = new DynamicParameters();
}
now before transaction.Commit() line I am assigning the value to my parameter _Param = p;
and I created a public method with return type of DynamicParameters like below
public DynamicParameters GetDynamicParameters()
{
return _Param;
}
and also added a code like below from where I am executing my common dapper class
SPResponse response = await _Dapper.ExecuteAsync("[dbo].[TemplateAdd]", _DynamicParameter);
if (response.ReturnStatus == "0")
{
DynamicParameters dp = _Dapper.GetDynamicParameters();
response.Ref1 = Convert.ToString(dp.Get<int>("#SP_ID"));
response.Ref2 = request.FileServerId;
}
This is the question of Binary Tree. Level: Easy
In the second code, in while loop I just stored the value of popped integer value from stack in int variables and then wrote the condition of if loop. But in first I did not stored them in any variables I directly used them in if condition of while loop. Can anyone please explain why is it creating a difference?
This was my approach, in this if the input trees are 333 and 333 then it gives "no"(trees are not identical).
`
class Solution
{
public void preOrder(Node root,Stack<Integer> stack){
if(root==null){
return ;
}
stack.push(root.data);
preOrder(root.left,stack);
preOrder(root.right,stack);
}
boolean isIdentical(Node root1, Node root2)
{
// Code Here
if(root1==null||root2==null)
return false;
Stack<Integer> stack1 = new Stack<>();
Stack<Integer> stack2 = new Stack<>();
preOrder(root1,stack1);
preOrder(root2,stack2);
if(stack1.size()!=stack2.size())
return false;
while(!stack1.isEmpty()&&!stack2.isEmpty()){
if(stack1.pop()!=stack2.pop())
return false;
}
return true;
}
}`
But, in this the same input trees(333 and 333) gave correct output i.e "yes".
` class Solution
{
public void preOrder(Node root,Stack<Integer> stack){
if(root==null){
return ;
}
stack.push(root.data);
preOrder(root.left,stack);
preOrder(root.right,stack);
}
boolean isIdentical(Node root1, Node root2)
{
// Code Here
if(root1==null||root2==null)
return false;
Stack<Integer> stack1 = new Stack<>();
Stack<Integer> stack2 = new Stack<>();
preOrder(root1,stack1);
preOrder(root2,stack2);
if(stack1.size()!=stack2.size())
return false;
while(!stack1.isEmpty()&&!stack2.isEmpty()){
int n1 = stack1.pop();
int n2 = stack2.pop();
if(n1!=n2)
return false;
}
return true;
}
}`
Lets say you are trying to access deeply nested children in a map and you are not able to expect their parents to be there. Example:
Map awesomeMap = {
"this":{
"is":{
"sometimes":"not here"
}
}
}
Map notAwesomeMap = {
"this":{
"haha":{
"we":"switched"
}
}
}
When I go to access notAwesomeMap['this']['is']['sometimes'] it will return an error because ['this']['is'] is null, and you cannot look for the value ['sometimes'] of null.
So that's fine, but I was hoping to be able to use conditional member access operators...
notAwesomeMap['this']?.['is']?.['sometimes']
but that doesn't work...
Short of wrapping everything in a try block, is there a good way to handle these situations?
Edit: I tried playing around with this and I didn't find anything really illuminating, but maybe this gives someone an idea
void main() {
Map nestedMap = {
'this':{
'is':{
'sometimes':'here'
}
}
};
final mapResult = nestedMap['this'];
print(mapResult); //returns {is: {sometimes: here}}
final nullResult = nestedMap['this']['is an'];
print(nullResult); // returns null
final nullifiedResult = nullify(nestedMap['this']['is an']['error']);
print(nullifiedResult); // returns error, but is this possible another way?
final errorResult = nestedMap['this']['is an']['error'];
print(errorResult); // returns error
}
nullify(object){
try {
final result = object;
return result;
}
catch (e) {
return null;
}
}
One way would be
final result = (((nestedMap ?? const {})['this'] ?? const {})['is an'] ?? const {})['error'];
See also Null-aware operator with Maps
You could write a simple function to help do what you want:
R lookup<R, K>(Map<K, dynamic> map, Iterable<K> keys, [R defaultTo]);
Example usage:
final result = lookup(inputMap, ['this', 'is', 'something']);
Example implementation:
https://dartpad.dartlang.org/1a937b2d8cdde68e6d6f14d216e4c291
void main() {
var nestedMap = {
'this':{
'is':{
'sometimes':'here'
}
}
};
print(lookup(nestedMap, ['this']));
print(lookup(nestedMap, ['this', 'is']));
print(lookup(nestedMap, ['this', 'is', 'sometimes']));
print(lookup(nestedMap, ['this', 'is', 'error']));
// Bail out on null:
print(lookup(nestedMap, ['error'], 'Default Value'));
}
R lookup<R, K>(Map<K, dynamic> map, Iterable<K> keys, [R defaultTo]) {
dynamic current = map;
for (final key in keys) {
if (current is Map<K, dynamic>) {
current = current[key];
} else {
return defaultTo;
}
}
return current as R;
}
I like #matanlurey's approach, but have made two changes:
Drop the defaultTo since you can still use ?? which is more readable.
Swallow type-cast errors.
R lookup <R, K>(Map<K, dynamic> map, Iterable<K> keys) {
dynamic current = map;
for (final key in keys) {
if (current is Map<K, dynamic>) {
current = current[key];
}
}
try{
return current as R;
} catch(e){
// do nothing
}
}
Usage is similar
String someValue = lookup(nestedMap, ['some', 'value']) ?? 'Default Value';
I'm trying to create a server-side Dart class that performs various data-related tasks. All of these tasks rely on the database having been first initialized. The problem is that the init of the database happens asynchronously (returns a Future). I first tried to put the init code into the constructor, but have given up on this approach as it seems to not be viable.
I am now attempting to figure out how to force the DB initialization as a first step in any method call that accesses data. So in other words, when attemptLogin() is called below, I'd like to first check if the DB has been initialized and initialize it if necessary.
However, there are two obstacles. If the database hasn't been initialized, the code is straightforward - initialize the db, then use the then() method of the returned future to do the rest of the function. If the db is not yet initialized, what do I attach my then() method to?
Second related question is what happens when a database is currently being initialized but this process is not yet complete? How can I pull in and return this "in-progress" Future?
This is the basic gist of the code I'm trying to wrangle:
class DataManager {
bool DbIsReady = false;
bool InitializingDb = false;
Db _db;
Future InitMongoDB() {
print("Initializing MongoDB");
InitializingDb = true;
_db = new Db("mongodb://127.0.0.1/test");
return _db.open().then((_) {
DbIsReady = true;
InitializingDb = false;
});
}
Future<List> attemptLogin(String username, String password) {
Future firstStep;
if ((!DbIsReady) && (!InitializingDb) {
Future firstStep = InitMongoDB()
}
else if (InitializingDb) {
// Need to return the InitMongoDB() Future that's currently running, but how?
}
else {
// How do I create a blank firstStep here?
}
return firstStep.then((_) {
users = _db.collection("users");
return // ... rest of code cut out for clarity
});
}
}
Thanks in advance for your help,
Greg
Just return
return new Future<bool>.value(true);
// or any other value instead of `true` you want to return.
// or none
// return new Future.value();
Just keep the future alive:
class DataManager {
Future _initializedDb;
Future initMongoDb() { ... }
Future<List> attemptLogin(String username, String password) {
if (_initializedDb == null) {
_initializedDb = initMongoDB();
}
return _initializedDb.then((db) {
users = db.collection("users");
return // ... rest of code cut out for clarity
});
}
}
You might need to pay attention for the error-case. It's up to you if you want to deal with errors in the initMongoDB or after it.
One of the possible solutions:
import "dart:async";
void main() {
var dm = new DataManager();
var selectOne = dm.execute("SELECT 1");
var selectUsers = dm.execute("SELECT * FROM users");
var users = selectOne.then((result) {
print(result);
return selectUsers.then((result) {
print(result);
});
});
users.then((result) {
print("Goodbye");
});
}
class Event {
List<Function> _actions = new List<Function>();
bool _raised = false;
void add(Function action) {
if (_raised) {
action();
} else {
_actions.add(action);
}
}
void raise() {
_raised = true;
_notify();
}
void _notify() {
if (_actions.isEmpty) {
return;
}
var actions = _actions.toList();
_actions.clear();
for (var action in actions) {
action();
}
}
}
class DataManager {
static const int _STATE_NOT_INITIALIZED = 1;
static const int _STATE_INITIALIZING = 2;
static const int _STATE_READY = 3;
Event _initEvent = new Event();
int _state = _STATE_NOT_INITIALIZED;
Future _init() {
if (_state == _STATE_NOT_INITIALIZED) {
_state = _STATE_INITIALIZING;
print("Initializing...");
return new Future(() {
print("Initialized");
_state = _STATE_READY;
_initEvent.raise();
});
} else if (_state == _STATE_INITIALIZING) {
print("Waiting until initialized");
var completer = new Completer();
_initEvent.add(() => completer.complete());
return completer.future;
}
return new Future.value();
}
Future execute(String query, [Map arguments]) {
return _init().then((result) {
return _execute(query, arguments);
});
}
Future _execute(String query, Map arguments) {
return new Future.value("query: $query");
}
}
Output:
Initializing...
Waiting until initialized
Initialized
query: SELECT 1
query: SELECT * FROM users
Goodbye
I think that exist better solution but this just an attempt to answer on your question (if I correctly understand you).
P.S. EDITED at 11 July 2014
Slightly modified (with error handling) example.
import "dart:async";
void main() {
var dm = new DataManager();
var selectOne = dm.execute("SELECT 1");
var selectUsers = dm.execute("SELECT * FROM users");
var users = selectOne.then((result) {
print(result);
return selectUsers.then((result) {
print(result);
});
});
users.then((result) {
print("Goodbye");
});
}
class DataManager {
static const int _STATE_NOT_INITIALIZED = 1;
static const int _STATE_INITIALIZING = 2;
static const int _STATE_READY = 3;
static const int _STATE_FAILURE = 4;
Completer _initEvent = new Completer();
int _state = _STATE_NOT_INITIALIZED;
Future _ensureInitialized() {
switch (_state) {
case _STATE_NOT_INITIALIZED:
_state = _STATE_INITIALIZING;
print("Initializing...");
new Future(() {
print("Initialized");
_state = _STATE_READY;
// throw null;
_initEvent.complete();
}).catchError((e, s) {
print("Failure");
_initEvent.completeError(e, s);
});
break;
case _STATE_INITIALIZING:
print("Waiting until initialized");
break;
case _STATE_FAILURE:
print("Failure detected");
break;
default:
print("Aleady intialized");
break;
}
return _initEvent.future;
}
Future execute(String query, [Map arguments]) {
return _ensureInitialized().then((result) {
return _execute(query, arguments);
});
}
Future _execute(String query, Map arguments) {
return new Future.value("query: $query");
}
}
For those that are still wondering how to create a blank Future in Dart and later complete them, you should use the Completer class like in the next example.
class AsyncOperation {
final Completer _completer = new Completer();
Future<T> doOperation() {
_startOperation();
return _completer.future; // Send future object back to client.
}
// Something calls this when the value is ready.
void finishOperation(T result) {
_completer.complete(result);
}
// If something goes wrong, call this.
void _errorHappened(error) {
_completer.completeError(error);
}
}
Future<Type> is non nullable in Dart, meaning that you have to initialize it to a value. If you don't, Dart throws the following error:
Error: Field should be initialized because its type 'Future<Type>' doesn't allow null.
To initialize a Future<Type>, see the following example:
Future<String> myFutureString = Future(() => "Future String");
Here "Future String" is a String and so the code above returns an instance of Future<String>.
So coming to the question of how to create a blank/empty Future, I used the following code for initializing an empty Future List.
Future<List> myFutureList = Future(() => []);
I found this link to be quite useful in understanding Futures in Flutter and Dart: https://meysam-mahfouzi.medium.com/understanding-future-in-dart-3c3eea5a22fb
In Dart, how would I best code the equivalent of an (immutable/value/non-object) out or reference parameter?
For example in C#-ish I might code:
function void example()
{
int result = 0;
if (tryFindResult(anObject, ref result))
processResult(result);
else
processForNoResult();
}
function bool tryFindResult(Object obj, ref int result)
{
if (obj.Contains("what I'm looking for"))
{
result = aValue;
return true;
}
return false;
}
This is not possible in Dart. Support for struct value types, ref or val keywords were discussed on the Dart mailing list just like week. Here is a link to the discussion where you should let your desire be known:
https://groups.google.com/a/dartlang.org/d/topic/misc/iP5TiJMW1F8/discussion
The Dart-way would be:
void example() {
List result = tryFindResult(anObject);
if (result[0]) {
processResult(result[1]);
} else {
processForNoResult();
}
}
List tryFindResult(Object obj) {
if (obj.contains("What I'm looking for")) {
return [true, aValue];
}
return [false, null];
}
you can also use a tuple package like tuple-2.0.0
add tuple: ^2.0.0
to your pubspec.yaml
then any function can return many typed objects like this:
import 'package:tuple/tuple.dart';
Tuple3<int, String, bool?>? returnMany() {
return ok ? Tuple3(5, "OK", null) : null;
}
var str = returnMany().item2;
In your case:
void example() {
var result = tryFindResult(anObject);
if (result.item1) {
processResult(result.item2!);
} else {
processForNoResult();
}
}
Tuple2<bool, int?> tryFindResult(Object obj) {
if (obj.contains("What I'm looking for")) {
return Tuple2(true, aValue);
}
return Tuple2(false, null);
}
you can throw an exception too when no result.
void example() {
var result = tryFindResult(anObject);
try {
processResult(result);
} on NullException catch(e){
processForNoResult();
}
}
int tryFindResult(Object obj) { // throws NullException
if (obj.contains("What I'm looking for")) {
return aValue;
}
throw NullException();
}