I have an Indy custom TCP Server and when I create the object I pass some string parameters (like name, password...) that are stored in the private section of the class. This is the only time when those fields are writen to (before I start the server). Every write makes a new copy of the string, not pass the reference, to be sure that those strings belongs only to this object. Now, after I start the server and receive some connections, it is safe to read those string fields in those new threads without adding some critical sections ? The values won't change in the time when that server is active...
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RX configuration
To configure an RX-PDO, three object categories in the object dictionary must be taken into account:
1-The objects that describe the functionality of the mapping.
2-The objects that describe the content of the mapping.
3-The objects that are to receive the received data. Configuration of the functionality (communication parameter)
The configuration of the first mapping is stored in the subindices of object 1400h. The second mapping is configured in 1401h and so on. In the following, we refer to 140Nh. Here, the configuration affects the COB-ID of the PDO message and the transfer type.
Objects 140Nh have only three subindices:
Subindex 0 (max. subindex): Total number of subindices
Subindex 1 (COB-ID): The COB-ID is stored here. For PDO mappings 1–4 (1600h–1603h), the CAN-ID is fixed depending on the node-ID and only the valid bit (bit 31) can be set in the COB-ID. From 1604h–1607h, the CAN-ID can be set independently (with the restriction that it not be used by other services, see table at the start of chapter CANopen services) as can the valid bit. The change of a COB-ID does not take effect until after the controller or communication is restarted
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According to the above content, where is object 140N in the Object Dictionary? And how should we communicate with it?
I was trying to write a smart contract that would use the same key name(the name of the person whose details I am storing) multiple times and want all of the entries made for that key-name to be output when querying for the name.
Is it possible on to do so on hyperledger? If yes, then how would you write the query function If not could you recommend an alternate method to achieve the same result?
I am new to hyperledger and have no idea how to proceed considering I didnt see any examples of chaincode similar to this.
What you need to do is to encode the value into JSON format and store it marshaled for the given key, for example you can define a struct with a slice, update/append slice each time with new value, marshal to byte array and then save into ledger.
Each update you read the byte array from the ledger unmarshal it back to struct, update with required information and save back with same key.
To retrieve history of changes you can use one of the methods from ChaincodeStubInterface
// Chaincode interface must be implemented by all chaincodes. The fabric runs
// the transactions by calling these functions as specified.
type ChaincodeStubInterface interface {
// Other methods omitted
// GetHistoryForKey returns a history of key values across time.
// For each historic key update, the historic value and associated
// transaction id and timestamp are returned. The timestamp is the
// timestamp provided by the client in the proposal header.
// GetHistoryForKey requires peer configuration
// core.ledger.history.enableHistoryDatabase to be true.
// The query is NOT re-executed during validation phase, phantom reads are
// not detected. That is, other committed transactions may have updated
// the key concurrently, impacting the result set, and this would not be
// detected at validation/commit time. Applications susceptible to this
// should therefore not use GetHistoryForKey as part of transactions that
// update ledger, and should limit use to read-only chaincode operations.
GetHistoryForKey(key string) (HistoryQueryIteratorInterface, error)
}
I have some data that I need to persist through multiple actions within my Grails app. Due to the nature of the data, I would prefer not to store the data in the session. Here is an example of what I would like to do.
class MyController{
def index(){
MyObject object = MyObject.new(params.first, params.second, params.third)
[gspObject:object]
}
def process(){
MyObject object = params.gspObject
//continue from here
}
}
In my GSP if I do
<g:form action="process" params="[gspObject:gspObject]">
Then I get the error
Cannot cast object 'net.package.MyObject#699c14d8' with class 'java.lang.String' to class 'net.package.MyObject'
My question is, If I want to get the object back that I sent to the gsp, how can I get that? Is there some kind of scope that I can save the object in that would be a little safer then session? Is there a way to pass the object into the page itself and pass it back in the next request?
Grails has many layers, but at the bottom you have plain old HTTP just like in any web app. It's a stateless protocol, and you send a text or binary response, and receive text or text + binary requests. But you can't expect to be able to send an arbitrary object to a web browser in HTML and receive it back again in the same state as when you sent it - where is this Java/Groovy JVM object going to be stored in the browser?
You have basically two options. One is to store it at the server, which is less work because it remains as the same object the whole time. The session is a good location because it's coupled to the user, is created on-demand and can automatically time out and be removed, etc. The other is to do what you're trying to do - send it to the client and receive it back - but you are going to have to serialize it from an object (which could be a complex object containing arbitrarily many other objects) and deserialize it from the format you used on the client back into Java/Groovy objects.
JSON is a good option for serialization/marshalling. You could store the stringified object in a hidden form element if your page uses a form, or in a querystring arg if you click a link from this page to the next in the workflow. Don't send all of the object's data though, only what you need to rebuild it. Anything that's available in the database should be referenced by id and reloaded.
Something like
[gspObject: object as JSON]
or
[gspObject: [first: object.first, first: object.firstsecond, ...] as JSON]
will get it in the correct format for sending, and then you can parse the JSON from the request to reinstantiate the instance.
I want to use the SqlEntityConnection type provider in f# to query and update a db.
It works well when I use it with the connection string pointing to a live SQL Server DataBase.
type EntityConnection = SqlEntityConnection<"Data Source=myServer;Initial Catalog=myDb;...", Pluralize=true>
Now I want to get rid of the dependency with the live DB and, instead, use a local schema file. Given what I read on msdn, I gave a try to the following line:
type private EntityConnection = SqlEntityConnection<LocalSchemaFile="mySchemaFile.ssdl", Pluralize=true>
Unfortunately, it doesn't compile and the compiler's message is:
Error 46 The type provider 'Microsoft.FSharp.Data.TypeProviders.DesignTime.DataProviders' reported an error: When using this provider you must specify either a connection string or a connection string name. To specify a connection string, use SqlEntityConnection<"...connection string...">.
So what should I do? If I leave the connection string, I have the feeling that I don't really turn off the dependency to the DB. For instance, if I try to switch the Data Source with a non-existing server, it doesn't compile.
You can provide a connection string name, along with a connection string in the configuration file.
You can still provide a localschemafile that will be used to cache locally the schema.
If you put the schema file under source control, the connection string will only be used as a default when calling GetDataContext() without parameter, but not when building or editing code.
You also need to set the parameter ForceUpdate to False.
I'm using a javascript plugin called jSignature to give my MVC4 application delivery signature capture functionality. jSignature outputs the signature info in a data:image/png;base64,iVBORw0KG... string format that looks to be around 32,000 characters long. I created a property in my model called DeliverySignature as a string and am able to save and retrieve the signature data but when I pull it back in from the database it's only about 5,000 characters long. What data type do I need to be using in my model's definition and in the action method (it's being passed in to a controller to save to the db) so that it preservers the complete string length? Thank you.
I would store it in varchar(max) column.
You can keep model property type of string as strings do not have a limited length.