I have a Hazelcast Map of HashMap as values as I have shown below.
HazelcastInstance client = HazelcastClient.newHazelcastClient(clientConfig);
IMap<String, HashMap<String, String>> imap = client.getMap("users");
HashMap<String, String> value = new HashMap<>();
value.put("name", "name-1");
value.put("email", "naame-1#gmail.com");
imap.set("1", value);
I want to perform a query using Predicates/SQLPredicate. How can I do that?
Please help me.
Unless there is a solid reason, you do not need to be storing a Map object as value. Looking at your code, you should rather create a simple POJO and store that as value. For predicates, check documentation here:
https://docs.hazelcast.org/docs/3.11.2/manual/html-single/index.html#distributed-query
There is no default built-in HashMap serializer for values, Hence, you need to write a wrapper object which implements one of the Hazelcast Serializations.
Related
I'm building an API with Nest.js and I've been using a mapper to convert the TypeORM entity to a DTO (and vice-versa).
Until now, I've been doing this manually:
public static async entityToDto(entity: UserEntity): Promise<UserDto> {
const dto = new UserDto();
dto.id = entity.id;
dto.emailAddress = entity.emailAddress;
dto.firstName = entity.firstName;
dto.lastName = entity.lastName;
dto.addressLine1 = entity.addressLine1;
dto.addressLine2 = entity.addressLine2;
dto.townCity = entity.townCity;
[...]
return dto;
}
In my opinion, this is a nice (albeit inflexible) approach. It explicitly controls which fields are returned to the user, minimizing the chance of leaking sensitive fields (like password hash). However, I was under the impression that the purpose of a DTO is to have a single place to modify data about something. If I needed to add a field, I'd have to modify both the DTO and the mapper.
It seems to be the convention to have one mapper per entity. However, if I don't want to return, for example, the accountStatus field, I would have to write a new mapper. So I have now multiple mappers which would need to be modified.
I had the idea to write a "universal" mapper which looks at the fields in the DTO, and maps them to the fields in the entity.
I'm relatively new to TypeScript and Nest.js, so I was wondering how others manage this.
I suggest you should try object property map built-in by typescript. Basically, your entity can be map to dto based on the similar property name like below
public static async entityToDto(entity: UserEntity): Promise<UserDto> {
const dto : UserDTO = ({
...entity,
additionalProperty: entity.someProperty
});
return dto;
}
Any property that sharing the same name between DTO and Entity will be mapped. It is far more clean and more flexible.
I want to convert my objects to hashmaps so I can use the Flutter method channels to send data to Android.
I've thought of iterating through and mapping them one by one, but there's got to be a more elegant way to do this...
Example:
Object
class Something {
Something(this.what, this.the, this.fiddle);
final String what;
final int the;
final bool fiddle;
}
Somewhere else
List<Something> listOStuff = List<Something>.generate(10, (int index){
return Something(index.toString(), index, false,);
});
List<Map<String, dynamic>> parseToMaps(List<Something> listOStuff){
List<Map<String, dynamic>> results;
// do something crazy to get listOStuff into Map of primitive values for each object
// preferably a built in method of some sort... otherwise, i guess i'll just iterate...
// maybe even an imported package if such thing exists
return results;
}
List<Map<String, dynamic>> listOMaps = parseToMaps(listOStuff);
Something like this in Java
You can use the map and return the object that you want:
List<Map<String, dynamic>> listOMaps = listOStuff
.map((something) => {
"what": something.what,
"the": something.the,
"fiddle": something.fiddle,
})
.toList();
I'm not sure what exactly you're looking for, but there is a way to have custom objects encoded without having to specify it directly when you call the method.
What you have to do is implement a MethodCodec and/or MessageCodec that defines how your object is encoded and decoded. The easiest way is probably to subclass StandardMethodCodec and/or StandardMessageCodec (it might be enough to override StandardMessageCodec and pass it to StandardMessageCodec).
If you implement read & write correctly for your object, then all you have to do is pass the list of objects directly to your method call and flutter will handle the encoding.
Note that there are corresponding classes on the Android & iOS sides of things that you could use to have the data decoded directly to objects, and in fact you might have to implement them to get things to work depending on how you do it.
I am using map in one of my table as below:
media map<UUID, frozen<map<int, varchar>>>
Alhough I was able to successfully insert/update into this map, couldn't read from it.
I am using datastax java driver 3.0.0
So far I have tried this:
Map<UUID, Map> media = row.getMap("media", UUID.class, Map.class);
But this line gives below exception:
com.datastax.driver.core.exceptions.CodecNotFoundException: Codec not found for requested operation: [map<int, varchar> <-> java.util.Map]
How can I read from this field?
You are trying to use GettableByNameData.getMap(String, Class, Class) method. Instead of that, to get complex data type like Map, you can use GettableByNameData.getMap(String, TypeToken, TypeToken) method.
import com.google.common.reflect.TypeToken;
TypeToken uuidToken = new TypeToken<UUID>() {};
TypeToken mapToken = new TypeToken<Map<Integer, String>>() {};
Map<UUID, Map<Integer, String>> media = row.getMap("media", uuidToken, mapToken);
EF 5.0, using code-first on existing database workflow.
Database has your basic SalesOrder and SalesOrderLine tables with required foreign key on the SalesOrderLine as follows;
public class SalesOrder
{
public SalesOrder()
{
this.SalesOrderLines = new List<SalesOrderLine>();
}
public int SalesOrderID { get; set; }
public int CustomerID { get; set; }
public virtual Customer Customer { get; set; }
public virtual ICollection<SalesOrderLine> SalesOrderLines { get; set; }
}
public class SalesOrderLine
{
public SalesOrderLine()
{
}
public int SalesOrderLineID { get; set; }
public int SalesOrderID { get; set; }
public virtual SalesOrder SalesOrder { get; set; }
}
public SalesOrderLineMap()
{
// Primary Key
this.HasKey(t => t.SalesOrderLineID);
// Table & Column Mappings
this.ToTable("SalesOrderLine");
this.Property(t => t.SalesOrderLineID).HasColumnName("SalesOrderLineID");
this.Property(t => t.SalesOrderID).HasColumnName("SalesOrderID");
// Relationships
this.HasRequired(t => t.SalesOrder)
.WithMany(t => t.SalesOrderLines)
.HasForeignKey(d => d.SalesOrderID);
}
Now according to this page:
http://msdn.microsoft.com/en-us/data/jj713564
...we are told that:
The following code removes a relationship by setting the foreign key
to null. Note, that the foreign key property must be nullable.
course.DepartmentID = null;
Note: If the reference is in the added state (in this example, the
course object), the reference navigation property will not be
synchronized with the key values of a new object until SaveChanges is
called. Synchronization does not occur because the object context does
not contain permanent keys for added objects until they are saved. If
you must have new objects fully synchronized as soon as you set the
relationship, use one of the following methods.
By assigning a new object to a navigation property. The following code
creates a relationship between a course and a department. If the
objects are attached to the context, the course is also added to the
department.Courses collection, and the corresponding foreign key
property on the course object is set to the key property value of the
department.
course.Department = department;
...sounds good to me!
Now my problem:
I have the following code, and yet both of the the Asserts fail - why?
using (MyContext db = new MyContext ())
{
SalesOrder so = db.SalesOrders.First();
SalesOrderLine sol = db.SalesOrderLines.Create();
sol.SalesOrder = so;
Trace.Assert(sol.SalesOrderID == so.SalesOrderID);
Trace.Assert(so.SalesOrderLines.Contains(sol));
}
Both objects are attached to the context - are they not? Do I need to do a SaveChanges() before this will work? If so, that seems a little goofy and it's rather annoying that I need to set all of the references on the objects by hand when a new object is added to a foreign-key collection.
-- UPDATE --
I should mark Gert's answer as correct, but I'm not very happy about it, so I'll wait a day or two. ...and here's why:
The following code does not work either:
SalesOrder so = db.SalesOrders.First();
SalesOrderLine sol = db.SalesOrderLines.Create();
db.SalesOrderLines.Add(sol);
sol.SalesOrder = so;
Trace.Assert(so.SalesOrderLines.Contains(sol));
The only code that does work is this:
SalesOrder so = db.SalesOrders.First();
SalesOrderLine sol = db.SalesOrderLines.Create();
sol.SalesOrder = so;
db.SalesOrderLines.Add(sol);
Trace.Assert(so.SalesOrderLines.Contains(sol));
...in other words, you have to set all of your foreign key relationships first, and then call TYPE.Add(newObjectOfTYPE)
before any of the relationships and foreign-key fields are wired up. This means that from the time the Create is done until the time you do the Add(), the object is basically in a half-baked state. I had (mistakenly) thought that since I used Create(), and since Create() returns a sub-classed dynamic object (as opposed to using "new" which returns a POCO object) that the relationships wire-ups would be handled for me. It's also odd to me, that you can call Add() on an object created with the new operator and it will work, even though the object is not a sub-classed type...
In other words, this will work:
SalesOrder so = db.SalesOrders.First();
SalesOrderLine sol = new SalesOrderLine();
sol.SalesOrder = so;
db.SalesOrderLines.Add(sol);
Trace.Assert(sol.SalesOrderID == so.SalesOrderID);
Trace.Assert(so.SalesOrderLines.Contains(sol));
...I mean, that's cool and all, but it makes me wonder; what's the point of using "Create()" instead of new, if you're always going to have to Add() the object in either case if you want it properly attached?
Most annoying to me is that the following fails;
SalesOrder so = db.SalesOrders.OrderBy(p => p.SalesOrderID).First();
SalesOrderLine sol = db.SalesOrderLines.Create();
sol.SalesOrder = so;
db.SalesOrderLines.Add(sol);
// NOTE: at this point in time, the SalesOrderId field has indeed been set to the SalesOrderId of the SalesOrder, and the Asserts will pass...
Trace.Assert(sol.SalesOrderID == so.SalesOrderID);
Trace.Assert(so.SalesOrderLines.Contains(sol));
sol.SalesOrder = db.SalesOrders.OrderBy(p => p.SalesOrderID).Skip(5).First();
// NOTE: at this point in time, the SalesOrderId field is ***STILL*** set to the SalesOrderId of the original SO, so the relationships are not being maintained!
// The Exception will be thrown!
if (so.SalesOrderID == sol.SalesOrderID)
throw new Exception("salesorderid not changed");
...that seems like total crap to me, and makes me feel like the EntityFramework, even in version 5, is like a minefield on a rice-paper bridge. Why would the above code not be able to sync the SalesOrderId on the second assignment of the SalesOrder property? What essential trick am I missing here?
I've found what I was looking for! (and learned quite a bit along the way)
What I thought the EF was generating in it's dynamic proxies were "Change-Tracking Proxies". These proxy classes behave more like the old EntityObject derived partial classes from the ADO.Net Entity Data Model.
By doing some reflection on the dynamically generated proxy classes (thanks to the information i found in this post: http://davedewinter.com/2010/04/08/viewing-generated-proxy-code-in-the-entity-framework/ ), I saw that the "get" of my relationship properties was being overridden to do Lazy Loading, but the "set" was not being overriden at all, so of course nothing was happening until DetectChanges was called, and DetectChanges was using the "compare to snapshot" method of detecting changes.
Further digging ultimately lead me to this pair of very informative posts, and I recommend them for anyone using EF:
http://blog.oneunicorn.com/2011/12/05/entity-types-supported-by-the-entity-framework/
http://blog.oneunicorn.com/2011/12/05/should-you-use-entity-framework-change-tracking-proxies/
Unfortunately, in order for EF to generate Change-Tracking Proxies, the following must occur (quoted from the above):
The rules that your classes must follow to enable change-tracking
proxies are quite strict and restrictive. This limits how you can
define your entities and prevents the use of things like private
properties or even private setters. The rules are: The class must be
public and not sealed. All properties must have public/protected
virtual getters and setters. Collection navigation properties must be
declared as ICollection<T>. They cannot be IList<T>, List<T>,
HashSet<T>, and so on.
Because the rules are so restrictive it’s easy to get something wrong and the result is you won’t get a change-tracking proxy. For example,
missing a virtual, or making a setter internal.
...he goes on to mention other things about Change-Tracking proxies and why they may show better or worse performance.
In my opinion, the change-tracking proxy classes would be nice as I'm coming from the ADO.Net Entity Model world, and I'm used to things working that way, but I've also got some rather rich classes and I'm not sure if I will be able to meet all of the criteria. Additionally that second bullet point makes me rather nervous (although I suppose I could just create a unit test that loops through all of my entities, does a Create(0 on each and then tests the resulting object for the IEntityWithChangeTracker interface).
By setting all of my properties to virtual in my original example I did indeed get IEntityWithChangeTracker typed proxy classes, but I felt a little ... I don't know... "dirty" ...for using them, so I think I will just have to suck it up and remember to always set both sides of my relationships when doing assignments.
Anyway, thanks for the help!
Cheers,
Chris
No, SalesOrderLine sol is not attached to the context (although it is created by a DbSet). You must do
db.SalesOrderLines.Add(sol);
to have it attached to the context in a way that the ChangeTracker executes DetectChanges() (DbSet.Add() is one of the methods that trigger this) and, thus, also executes relationship fixup, which sets sol.SalesOrderID and ensures that so.SalesOrderLines contains the new object.
So, no, you don't need to execute SaveChanges(), but the object must be added to the context and relationship fixup must have been triggered.
In jcouchdb I used to extend BaseDocument and then, in a transparent manner, mix Annotations and not declared fields.
Example:
import org.jcouchdb.document.BaseDocument;
public class SiteDocument extends BaseDocument {
private String site;
#org.svenson.JSONProperty(value = "site", ignoreIfNull = true)
public String getSite() {
return site;
}
public void setSite(String name) {
site = name;
}
}
and then use it:
// Create a SiteDocument
SiteDocument site2 = new SiteDocument();
site2.setProperty("site", "http://www.starckoverflow.com/index.html");
// Set value using setSite
site2.setSite("www.stackoverflow.com");
// and using setProperty
site2.setProperty("description", "Questions & Answers");
db.createOrUpdateDocument(site2);
Where I use both a document field (site) that is defined via annotation and a property field (description) not defined, both get serialized when I save document.
This is convenient for me since I can work with semi-structured documents.
When I try to do the same with Ektorp I have documents using annotations and Documents using HashMap BUT I couldn't find an easy way of getting the mix of both (I've tried using my own serializers but this seems to much work for something that I get for free in jcouchdb). Also tried to annotate a HashMap field but then is serialized as an object and I get the fields automatically saved BUT inside an object with the name of the HashMap field.
Is it possible to do (easily/for free) using Ektorp?
It is definitely possible. You have two options:
Base your class on org.ektorp.support.OpenCouchDbDocument
Annotate the you class with #JsonAnySetter and #JsonAnyGetter. Red more here: http://wiki.fasterxml.com/JacksonFeatureAnyGetter