So I run golang appengine with go endpoints package ...
I use structs to marshal and un marshal my json incoming requests and out going responses ..
type BusinessWorker struct {
Wid string `json:"wid" datastore:"Worker_id" endpoints:"req,desc=Worker id. string value"`
Phone string `json:"phone" datastore:"Phone" endpoints:"req,desc=Worker phone number. string value"`
}
So as you can see after I validate the data this obj is saved or loaded to/from the datastore ..
My question is ..
there are many cases I dont want to respond with all my data that is saved in the datastore .. is there some sort of attribute that I can give to the param that i dont wanna include in my response only in my incoming requests ?
It seems so elementary .. and I cant find it .. ?
Maybe you would like to try one or a combination of the following approaches:
Tag of "-" so that the field is ignored. e.g. json:"-"
omitempty can be included in your 'json:' and will cause the field not to be included in the resulting json. So you could set the fields you want to hide to nil, prior to serializing to json. e.g. json:"myName,omitempty"
copier - there are some projects like: jinzhu's copier that would allow you to copy your entity to a simplified structure, or you could roll your own. (a combination of JSON un-marshalling and marshalling can produce similar results).
For more details about the JSON package see Golang Json marshal docs
Related
We receive a JSON object from network along with a hash value of the object. In order to verify the hash we need to turn that JSON into a string and then make a hash out of it while preserving the order of the elements in the way they are in the JSON.
Say we have:
[
{"site1":
{"url":"https://this.is.site.com/",
"logoutURL":"",
"loadStart":[],
"loadStop":[{"someMore":"smthelse"}],
"there's_more": ... }
},
{"site2":
....
}
]
The Android app is able to get same hash value, and while debugging it we fed same simple string into both algorithms and were able to get out same hash out of it.
The difference that is there happens because of the fact that dictionaries are unordered structure.
While debugging we see that just before feeding a string into a hash algorithm, the string looks like the original JSON, just without the indentations, which means it preserves the order of items in it (on Android that is):
[{"site1":{"url":"https://this.is.site.com/", ...
While doing this with many approaches by now I'm not able to achieve the same: string that I get is different in order and therefore results in a different hash. Is there a way to achieve this?
UPDATE
It appears the problem is slightly different - thanks to #Rob Napier's answer below: I need a hash of only a part of incoming string (that has JSON in it), which means for getting that part I need to first parse it into JSON or struct, and after that - while getting the string value of it - the order of items is lost.
Using JSONSerialization and JSONDecoder (which uses JSONSerialization), it's not possible to reproduce the input data. But this isn't needed. What you're receiving is a string in the first place (as an NSData). Just don't get rid of it. You can parse the data into JSON without throwing away the data.
It is possible to create JSON parsers from scratch in Swift that maintain round-trip support (I have a sketch of such a thing at RNJSON). JSON isn't really that hard to parse. But what you're describing is a hash of "the thing you received." Not a hash of "the re-serialized JSON."
I am using the Yason library in common-lisp, I want to parse a json string but would like the parser to keep one a its node unparsed.
Typically with an example like that:
{
"metadata1" : "mydata1",
"metadata2" : "mydata2",
"payload" : {...my long payload object},
"otherNodesToParse" : {...}
}
How can I set the yason parser to parse my json but skip the payload node and keep it as a string in the json format.
Use: let's say I just want the envelope data (everything that's not the payload), and to forward the payload as-is (as json string) to another system.
If I parse the whole json (so including payload) and then re-encode the payload to json, it is inefficient. The payload size could also be pretty big.
How do you know where the end of the payload object is in the stream? You do so by parsing the stream: if you don't parse the stream you simply can't know where the end of the object is: that's the nature of JSON's syntax (as it is the nature of CL's default syntax). For instance the only way you can know the difference between where to continue after
{x:1}
and after
{x:1.2}
is by parsing the two things.
So you must necessarily parse the whole thing.
So the answer to your question is: you can't do this.
You could (but not, I think, with YASON) decide that you did not want to build an object as a result of the parse. And perhaps, if the stream you are parsing corresponds to something with random access like a string or a file, you could note the start and end positions in the stream to later extract a string from it corresponding to the unparsed data (or you could perhaps build it up as you go).
It looks as if some or all of this might be possible with CL-JSON, but you'd have to work at it.
Unless the objects you are reading are vast the benefit of this seems questionable-to-none. If you really do want to do something like this efficiently you need a serialisation scheme which tells you how long things are.
I am building a REST API which creates a resource. The resource has only one attribute which is a rather long and unique string. I am planning to send this data to the API as JSON. I see two choices for modeling the data as JSON
A primitive JSON String data type
A JSON object with one String attribute.
Both the options work.
Which of these two options is preferred for this context? And why?
Basic Answer for Returning
I would personally use option 2, which is: `A JSON object with one String attribute.'
Also, in terms of design: I prefer to return an object, that has a key/value. The key is also a name that provides context as to what has been returned.
Returning just a string, basically a "" or {""} lacks that context ( the name of the returned variable.
Debate: Are primitive Strings Json Objects?
There seems to be also some confusion as to if a String by itself is a valid JSON document.
This confusion and debate, are quite evident in the following posts where various technical specs are mentioned: Is a primitive type considered JSON?
The only thing for sure is that a JSON object with a key-value pair is definitely valid!
As to a string by itself.. I'm not sure ( requires more reading).
Update: Answer In terms of creating/updating an entity (Post/Put)
In the specific case above, relating to such a large string that "runs into a few kilobytes"... my feeling is that this would be included within the request body.
In the specific context of sending data, I would actually be comfortable with using either 1 or 2. Additionally, 1 seems more optimized ( if your frameworks support it), since the context about what the data is, is related to the rest API method.
However, if in the future you need to add one more parameter, you will have to use a JSON entity with more than one key.
The majority of my development experience has been from dynamically typed languages like PHP and Javascript. I've been practicing with Golang for about a month now by re-creating some of my old PHP/Javascript REST APIs in Golang. I feel like I'm not doing things the Golang way most of the time. Or more generally, I'm not use to working with strongly typed languages. I feel like I'm making excessive use of map[string]interface{} and slices of them to box up data as it comes in from http requests or when it gets shipped out as json http output. So what I'd like to know is if what I'm about to describe goes against the philosophy of golang development? Or if I'm breaking the principles of developing with strongly typed languages?
Right now, about 90% of the program flow for REST Apis I've rewritten with Golang can be described by these 5 steps.
STEP 1 - Receive Data
I receive http form data from http.Request.ParseForm() as formvals := map[string][]string. Sometimes I will store serialized JSON objects that need to be unmarshaled like jsonUserInfo := json.Unmarshal(formvals["user_information"][0]) /* gives some complex json object */.
STEP 2 - Validate Data
I do validation on formvals to make sure all the data values are what I expect before using it in SQL queries. I treat everyting as a string, then use Regex to determine if the string format and business logic is valid (eg. IsEmail, IsNumeric, IsFloat, IsCASLCompliant, IsEligibleForVoting,IsLibraryCardExpired etc...). I've written my own Regex and custom functions for these types of validations
STEP 3 - Bind Data to SQL Queries
I use golang's database/sql.DB to take my formvals and bind them to my Query and Exec functions like this Query("SELECT * FROM tblUser WHERE user_id = ?, user_birthday > ? ",formvals["user_id"][0], jsonUserInfo["birthday"]). I never care about the data types I'm supplying as arguments to be bound, so they're all probably strings. I trust the validation in the step immediately above has determined they are acceptable for SQL use.
STEP 4 - Bind SQL results to []map[string]interface{}{}
I Scan() the results of my queries into a sqlResult := []map[string]interface{}{} because I don't care if the value types are null, strings, float, ints or whatever. So the schema of an sqlResult might look like:
sqlResult =>
[0] {
"user_id":"1"
"user_name":"Bob Smith"
"age":"45"
"weight":"34.22"
},
[1] {
"user_id":"2"
"user_name":"Jane Do"
"age":nil
"weight":"22.22"
}
I wrote my own eager load function so that I can bind more information like so EagerLoad("tblAddress", "JOIN ON tblAddress.user_id",&sqlResult) which then populates sqlResult with more information of the type []map[string]interface{}{} such that it looks like this:
sqlResult =>
[0] {
"user_id":"1"
"user_name":"Bob Smith"
"age":"45"
"weight":"34.22"
"addresses"=>
[0] {
"type":"home"
"address1":"56 Front Street West"
"postal":"L3L3L3"
"lat":"34.3422242"
"lng":"34.5523422"
}
[1] {
"type":"work"
"address1":"5 Kennedy Avenue"
"postal":"L3L3L3"
"lat":"34.3422242"
"lng":"34.5523422"
}
},
[1] {
"user_id":"2"
"user_name":"Jane Do"
"age":nil
"weight":"22.22"
"addresses"=>
[0] {
"type":"home"
"address1":"56 Front Street West"
"postal":"L3L3L3"
"lat":"34.3422242"
"lng":"34.5523422"
}
}
STEP 5 - JSON Marshal and send HTTP Response
then I do a http.ResponseWriter.Write(json.Marshal(sqlResult)) and output data for my REST API
Recently, I've been revisiting articles with code samples that use structs in places I would have used map[string]interface{}. For example, I wanted to refactor Step 2 with a more standard approach that other golang developers would use. So I found this https://godoc.org/gopkg.in/go-playground/validator.v9, except all it's examples are with structs . I also noticed that most blogs that talk about database/sql scan their SQL results into typed variables or structs with typed properties, as opposed to my Step 4 which just puts everything into map[string]interface{}
Hence, i started writing this question. I feel the map[string]interface{} is so useful because majority of the time,I don't really care what the data is and it gives me to the freedom in Step 4 to construct any data schema on the fly before I dump it as JSON http response. I do all this with as little code verbosity as possible. But this means my code is not as ready to leverage Go's validation tools, and it doesn't seem to comply with the golang community's way of doing things.
So my question is, what do other golang developers do with regards to Step 2 and Step 4? Especially in Step 4...do Golang developers really encourage specifying the schema of the data through structs and strongly typed properties? Do they also specify structs with strongly typed properties along with every eager loading call they make? Doesn't that seem like so much more code verbosity?
It really depends on the requirements just like you have said you don't require to process the json it comes from the request or from the sql results. Then you can easily unmarshal into interface{}. And marshal the json coming from sql results.
For Step 2
Golang has library which works on validation of structs used to unmarshal json with tags for the fields inside.
https://github.com/go-playground/validator
type Test struct {
Field `validate:"max=10,min=1"`
}
// max will be checked then min
you can also go to godoc for validation library. It is very good implementation of validation for json values using struct tags.
For STEP 4
Most of the times, We use structs if we know the format and data of our JSON. Because it provides us more control over the data types and other functionality. For example if you wants to empty a JSON feild if you don't require it in your JSON. You should use struct with _ json tag.
Now you have said that you don't care if the result coming from sql is empty or not. But if you do it again comes to using struct. You can scan the result into struct with sql.NullTypes. With that also you can provide json tag for omitempty if you wants to omit the json object when marshaling the data when sending a response.
Struct values encode as JSON objects. Each exported struct field
becomes a member of the object, using the field name as the object
key, unless the field is omitted for one of the reasons given below.
The encoding of each struct field can be customized by the format
string stored under the "json" key in the struct field's tag. The
format string gives the name of the field, possibly followed by a
comma-separated list of options. The name may be empty in order to
specify options without overriding the default field name.
The "omitempty" option specifies that the field should be omitted from
the encoding if the field has an empty value, defined as false, 0, a
nil pointer, a nil interface value, and any empty array, slice, map,
or string.
As a special case, if the field tag is "-", the field is always
omitted. Note that a field with name "-" can still be generated using
the tag "-,".
Example of json tags
// Field appears in JSON as key "myName".
Field int `json:"myName"`
// Field appears in JSON as key "myName" and
// the field is omitted from the object if its value is empty,
// as defined above.
Field int `json:"myName,omitempty"`
// Field appears in JSON as key "Field" (the default), but
// the field is skipped if empty.
// Note the leading comma.
Field int `json:",omitempty"`
// Field is ignored by this package.
Field int `json:"-"`
// Field appears in JSON as key "-".
Field int `json:"-,"`
As you can analyze from above information given in Golang spec for json marshal. Struct provide so much control over json. That's why Golang developer most probably use structs.
Now on using map[string]interface{} you should use it when you don't the structure of your json coming from the server or the types of fields. Most Golang developers stick to structs wherever they can.
I imagine there must me a solution for this, I haven't found one however.
I receive JSON responses of this structure:
{
description: SomeString,
type: ACTIVITY,
timestamp: 1224043200000,
creationTime: 1224043200000,
userIdentification: 1111-2222-3333,
value: 2000
}
"Activity" is the name of my CoreData entity. How do I map this JSON to my data model? All examples I found so far assume a JSON similar to this format:
{
activity: {
description: SomeString,
timestamp: 1224043200000,
creationTime: 1224043200000,
userIdentification: 1111-2222-3333,
value: 2000
}
}
I'm assuming that you have multiple possible different types, each with an associated entity...
Define a mapping for each entity. Don't connect these directly to the response descriptors. Instead, create an RKDynamicMapping instance with a block (setObjectMappingForRepresentationBlock:, or a matcher) which checks the type of the data coming in and returns the appropriate mapping.
If your responses contain multiple different types in a single response then you may want to look at combining the above with KVC validation to reject any objects created with the wrong type. You would also need some different response descriptors or something to apply each of the different entity mappings...
You can look in the ObjectMapping section of the RestKit repo on github. To map your json response you can make use of the nil keyPath as explained here https://github.com/RestKit/RestKit/wiki/Object-mapping#mapping-values-without-key-paths.
As Wain said, you should use Dynamic Mapping to decide which class will be mapped with the json object that you are receiving depending on the value that certain attribute have. How to use Dynamic Mapping is explained here: https://github.com/RestKit/RestKit/wiki/Object-mapping#dynamic-object-mapping. I know it's late, but this could help somebody in the future.