In RTKQ-documentation example cacheKey is undefined, but usually that is not the case. My current solution is to save cacheKey in a slice which makes it available both to selectFromResult and onQueryStarted (essentially everywhere) but I feel it is less than perfect. Is there some recommended way of storing and reusing cacheKey in RTKQ?
I think you might be using wrong terms here. cacheKey is an internal string representation of your argument and you will never interact with that string in RTK-Query.
You will need the same argument in some cases.
In onQueryStarted of a query, you might just be able updateCachedData from the lifecylce api, so you do not need the argument.
For selectFromResult, you will need to pass the same argument into the hook as you did elsewhere. In that case, you can either pass it down to a child using props or share it using Redux state.
Related
I have an object that was created with GetxController and it has a list field. I want to select a specific item in that list and change some parameters. But I should be able to cancel this changing scenario. Because when I select an item and change it, also change that class list item.
In Dart, objects pass by reference. But I need to pass it by value for canceling change. There's any way to pass an object instance by value?
In this kind of scenario, you should try to use immutable types.
There are good Dart libraries for that, even if the language doesn't have native support for it... with truly immutable data types, you essentially get pass-by-value semantics. They also make it easy to make copies of your data with small modifications on the returned value (while the original obviously remains unmodified).
Example packages you could use:
built_collection
built_value
freezed
No.
But you can just make a copy yourself and pass that. And depending on whether the change was confirmed you can eiter copy it back into your list or not.
What does = do here?
List<Segment> totalSegments = flight.departureFlight.segments;
Do both, totalSegments and flight.departureFlight.segments point to the same memory reference or totalSegments has the same data as flight.departureFlight.segments but points to a different memory location?
My understanding was that the latter should happen since dart is pass by value and not reference. However, a very annoying bug occurred when I added this line below that one:
totalSegments.addAll(flight.returnFlight.segments);
This above line actually modified the flight variable which in turn somehow modified the AsyncSnapshot from the StreamBuilder. Although, I wasn't using the variable anywhere else and not modifying other variables mentioned.
This all happened inside build function of a Stateless Widget. Maybe that has to do something with it.
I tried reading dart documentation for it, but either I couldn't find what I am looking for or the information is simply missing there. Read this too, but according to this, my use case shouldn't happen.
When it comes to objects as in your case, you are assigning a reference to an existing object (memory location) to a new variable. While acting upon that reference, you change the same object.
If this is not what you intend, check out answers related to (deep) copying of the objects
You were mistaken by the fact that Dart passes by value, and not by reference. Actually, it is exactly the opposite: (Almost) everything is always passed by reference (Which is usually a good thing!) Therefore, it is quite logical that because you edited totalSegments your departureflight.segments got edited too. It is a synonym. One of the ways to solve your problem would be:
List<Segment> totalSegments = List();
totalSegments.addAll(flight.departureFlight.segments.toList());
List<Segment> totalSegments = flight.departureFlight.segments;
This expression does the following.
Assigns the value of the expression flight.departureFlight.segments to variable totalSegments.
This and only this and nothing more.
There is no need to know what is really happening, because this is what happens.
P.S.
What value will be obtained as a result of executing the expression flight.departureFlight.segments is another question, because it depends on the implementation of the members of the operands of the expression flight.departureFlight.segments.
How do I read the bind parameters inside a MyBatis Interceptor? I'm trying to extract those information so I can write them to a log table.
The guide (http://www.mybatis.org/mybatis-3/configuration.html) didn't mention how to get them, and the JavaDoc (http://www.mybatis.org/mybatis-3/es/apidocs/org/apache/ibatis/mapping/BoundSql.html) does not have a single line of comment. I saw an example on SO about constructing a new BoundSql but that isn't what I needed.
I tried to test what contents are stored in BoundSql.getParameterMappings() and BoundSql.getParameterObject(), but it seems to be pretty complex. There's JavaType and JdbcType, and if there's only one parameter the ParameterObject isn't a Map object.
What is the proper way to get the bind parameters from BoundSql?
After going through MyBatis source code (where comment is an endangered species), I found out how MyBatis processes the bind parameters. However, that requires access to the JDBC Statement object, which is simply not available inside an Interceptor.
Then I did some testing and settled on this:
If there is only a single parameter, BindSql.getParameterObject() will give you the parameter itself. By using BindSql.getParameterMappings() and ParameterMapping.getJavaType() I can tell which Java class the parameter is.
If there are more than one parameter, BindSql.getParameterObject() will return an instance of org.apache.ibatis.binding.MapperMethod.ParamMap, which extends HashMap, or it will be an instance of the DTO you used. Using .getProperty() from ParameterMapping as key or as getter name, you can process the bind parameters one by one.
If anyone has a better way to do this, I'm all ears.
I'm attempting to parse json from the GitHub API with play-json, and encountering a problem with the merge_commit_sha field on Pull Requests (incidentally, I know this field is deprecated, but don't want to discuss that in this parsing problem!). Unfortunately merge_commit_sha field comes back as the empty string in some cases:
"merge_commit_sha": ""
This is how the field is declared in my case class:
merge_commit_sha: Option[ObjectId],
I have an implicit Format[ObjectId], which does not tolerate the empty string, because that's not a valid value for a Git hash id. I'm also using a play-json macro-generated Read[PullRequest], which I'd like to keep on using, in preference to individually declaring reads for every single field on pull requests.
As I've declared the field to be an Option, I'd like "merge_commit_sha": "" to be read as the value None, but this is not what currently happens - a string is present, so the Format[ObjectId] is invoked, and returns a JsFailure.
One thing I tried was declaring an implicit Format[Option[ObjectId]] with the required behaviour, but it didn't seem to get used by the macro-generated Read[PullRequest].
You can define a custom Reads and Writes yourself.
Using Json.format[MyType] uses a Scala macro. You may be able to hook into that. Although, 'extending' a macro for this one case class just seems wrong.
Custom Reads and Writes might be a little 'boilerplate-like' and boring, but they have their upsides.
For example if your json has a bunch of new fields on it, you wont get a JsError when validating or transforming it to a case class. You only take what you need from the JSON and create objects. It also allows for a separation between your internal model and what you're consuming, which in some cases is preferred.
I hope this helps,
Rhys
EDIT
After using some other JSON libs I may have found what you are looking for.
I know the question was asking specifically after Play JSON.
If you're able to move away from Play JSON, Look at spray-json-shapeless specifically JsNullBehaviour and JsNullNotNone REF.
How can I pass a null constuctor argument using Castle Windsor? I thought the following would work
<parameters>
<repository>null</repository>
<message>null</message>
</parameters>`
If you want them to be null, it means that they are non-essential dependencies. By having them as ctor arguments you suggest otherwise. You should redesign your class to have another constructor that takes only essential dependencies, if you wish that they not change throughout the lifetime of an object (be readonly), or expose them as properties.
With Windsor you can't make it to pass nulls, for reasons mentioned in the other answer.
Wouldn't it better to simply have an additional public constructor that doesn't take these parameters, then you wouldn't need to register the parameters in the config?
This was discussed a while back on the mail list, and at the time I looked into the code. Null values are deliberately filtered out (mainly because the complicate type resolution).
I couldn't find a simple way to make a special case to add them.