I have a typical function that takes a post request from the frontend and decodes the data into a struct in order to put it into a psql database. You can see the code below. My problem is that I want to be able to abstract this function so that I can give it any amount of variables of any type so that for every request I don't have to have a separate write handler.
It looks difficult because I would have to somehow pass in a way to abstract var profitReq profitReq to work for any struct. If golang had some sort of eval string method I would know how to do this, but someone correct me if I'm wrong, but I don't think that it does.
The other place I need to change is in QueryRow - I have to be able to pass it in a variable number of variables. I could construct the string easily enough, but I'm not sure how to append variables to that QueryRow necessarily. If I append all the variables to an array for example, I can't pass that array into QueryRow as that's not how it's structured. Again, here some sort of eval statement would help.
I'm new to golang, but I've seen a lot of cool things related to interfaces, which I admittedly don't understand very well. Would there be a way to use an interface here that would help?
Thanks to anyone who can help!
func Write_profit_table(profitWriteChannel chan string, profitType string, req *http.Request) {
var profitReq profitReq;
err := json.NewDecoder(req.Body).Decode(&profitReq);
if err!=nil{
log.Panic(err)
}
NotInDB, _ := Search_userinfo_table(profitReq.Email)
if NotInDB == false {
var lastInsertId int
err2 := db.QueryRow("INSERT INTO profit(email, type, dateArray, amount, interest, compounded, recurring, name, description, profitFrom)
VALUES($1, $2, $3, $4, $5, $6, $7, $8, $9, $10) returning uid;",
profitReq.Email, profitReq.Type, pq.Array(profitReq.DateArray), profitReq.Profit, profitReq.Interest,
profitReq.Compounded, profitReq.Recurring, profitReq.Name, profitReq.Description, profitReq.ProfitFrom).Scan(&lastInsertId);
if err2!=nil{
log.Panic(err2)
}
}
profitWriteChannel<-"finished writing to profit"
}
The feature you're looking for is called generics.
Generics are not supported by Go 1.x
Luckily for us, there's a proposal for them for Go 2 (called Contracts)
What can you do until then?
Duplicate your code (probably what you're doing now)
Use interfaces
If you know that this method will always query by email, you could create simple interface for that purpose: type Emailer interface { Email() string }
Use empty interface (interface{}) and reflection to figure out what columns you have.
Write your own generator. A bit like (1), but you don't have to do this yourself.
Here's the gist of it:
https://play.golang.org/p/A_2YKWLvmn-
Related
I am looking for examples of Chapel passing by reference. This example works but it seems like bad form since I am "returning" the input. Does this waste memory? Is there an explicit way to operate on a class?
class PowerPuffGirl {
var secretIngredients: [1..0] string;
}
var bubbles = new PowerPuffGirl();
bubbles.secretIngredients.push_back("sugar");
bubbles.secretIngredients.push_back("spice");
bubbles.secretIngredients.push_back("everything nice");
writeln(bubbles.secretIngredients);
proc kickAss(b: PowerPuffGirl) {
b.secretIngredients.push_back("Chemical X");
return b;
}
bubbles = kickAss(bubbles);
writeln(bubbles.secretIngredients);
And it produces the output
sugar spice everything nice
sugar spice everything nice Chemical X
What is the most efficient way to use a function to modify Bubbles?
Whether Chapel passes an argument by reference or not can be controlled by the argument intent. For example, integers normally pass by value but we can pass one by reference:
proc increment(ref x:int) { // 'ref' here is an argument intent
x += 1;
}
var x:int = 5;
increment(x);
writeln(x); // outputs 6
The way that a type passes when you don't specify an argument is known as the default intent. Chapel passes records, domains, and arrays by reference by default; but of these only arrays are modifiable inside the function. ( Records and domains pass by const ref - meaning they are passed by reference but that the function they are passed to cannot modify them. Arrays pass by ref or const ref depending upon what the function does with them - see array default intent ).
Now, to your question specifically, class instances pass by "value" by default, but Chapel considers the "value" of a class instance to be a pointer. That means that instead of allowing a field (say) to be mutated, passing a class instance by ref just means that it could be replaced with a different class instance. There isn't currently a way to say that a class instance's fields should not be modifiable in the function (other than making them to be explicitly immutable data types).
Given all of that, I don't see any inefficiencies with the code sample you provided in the question. In particular, here:
proc kickAss(b: PowerPuffGirl) {
b.secretIngredients.push_back("Chemical X");
return b;
}
the argument accepting b will receive a copy of the pointer to the instance and the return b will return a copy of that pointer. The contents of the instance (in particular the secretIngredients array) will remain stored where it was and won't be copied in the process.
One more thing:
This example works but it seems like bad form since I am "returning" the input.
As I said, this isn't really a problem for class instances or integers. What about an array?
proc identity(A) {
return A;
}
var A:[1..100] int;
writeln(identity(A));
In this example, the return A in identity() actually does cause a copy of the array to be made. That copy wasn't created when passing the array in to identity(), since the array was passed by with a const ref intent. But, since the function returns something "by value" that was a reference, it's necessary to copy it as part of returning. See also arrays return by value by default in the language evolution document.
In any case, if one wants to return an array by reference, it's possible to do so with the ref or const ref return intent, e.g.:
proc refIdentity(ref arg) ref {
return arg;
}
var B:[1..10] int;
writeln(refIdentity(B));
Now there is no copy of the array and everything is just referring to the same B.
Note though that it's currently possible to write programs that return a reference to a variable that no longer exists. The compiler includes some checking in that area but it's not complete. Hopefully improvements in that area are coming soon.
I'm new to golang and am trying to understand a code example of type wrapping for the "non-atomic" type time.Time.
The type extension in question is from the Go client for GDAX on github, go-coinbase-exchange project.
The expected behavior would be for Time variables from the project (coinbase.Time), which are of type Time time.Time (as defined in the project's time.go file) to behave something like the following example for extending the "atomic" type int (from blog.riff.org in that they might follow a kind of "inheritance" from the base type for functions like Time.format (from golang's standard implementation of time:
package main
import "fmt"
type Int int
func (i Int) Add(j Int) Int {
return i + j
}
func main() {
i := Int(5)
j := Int(6)
fmt.Println(i.Add(j))
fmt.Println(i.Add(j) + 12)
}
But if I modify the code example from the project's List Account Ledger example found in Readme.md to include a print function which might otherwise give me a human-readable view of the CreatedAt struct variables (as follows), I get a compiler error saying that "type coinbase.Time has no field or method Format":
for _, e := range ledger {
print("Entry Creation: ")
fmt.Printf(e.CreatedAt.Format("2006-01-02 15:04:05.999999+00"))
}
The expected behavior inside the for loop would be for it to print the ledger entries in a human-readable format. I can get the contents of the structs, but I'm not really sure how to then use the resulting wall, ext and loc members.
For example, inserting fmt.Printf("%#v", e.CreatedAt) into the for loop gives me a representation of the time that looks something like this:
coinbase.Time{wall:0x3015a123, ext:63612345678, loc:(*time.Location)(nil)}
{806986000 63638738354 <nil>}
I can also see that wall is of type uint64, that ext is of type int64 and that loc is just GMT/UTC=0 by formatting the variable as a string because fmt.Printf("%s", e.CreatedAt) gives me output which is similar to the following:
{%!s(uint64=712345678) %!s(int64=63612345678) %!s(*time.Location=<nil>)}
It seems like I'm missing something. I've requested further information through issues tab on github, but maybe this is a nube question. So I'm not sure how quick the response time would be, and I'm interested in the more general case for extending non-atomic types in go.
Named types do not inherit any methods from the underlying type (indeed there is no inheritance at all in Go); you must cast to the underlying type to call any methods from that type:
(time.Time(e.CreatedAt)).Format("2006-01-02 15:04:05.999999+00")
Given the input value:
input =
name:'Foo'
id:'d4cbd9ed-fabc-11e6-83e6-307bd8cc75e3'
ref:5
addtData:'d4cbd9ed-fabc-11e6-83e6-307bd8cc75e3'
data:'bar'
When I try to destructure the input via a function like this:
simplify: (input)->
{ name, ref, id } = input
...the return value is still the full input or a copy of the input.
Am I missing something simple here? How can I access the destructured value. If you can't access the value via a return, it seems that destructuring has little value outside of locally scoped values.
While this isn't necessarily an advantage, the only way I was able to transpile and get the correct answer was to assign the destructure values to the local scope using # (aka this).
input =
name:'foo'
data:'bar'
id: 12314
key:'children'
ref:1
f = (input)->
{ #name, #id } = input
r = {}
f.call(r, input)
console.log r # Object {name: "foo", id: 12314}
working example - link
If someone has a better way to approach this, please add an answer so I can select it as this doesn't seem like the best way.
This is the query I am trying to run in PostgreSQL:
SELECT * FROM message WHERE id IN (
SELECT unnest(message_ids) "mid"
FROM session_messages WHERE session_id = '?' ORDER BY "mid" ASC
);
However, I am not able do something:
create.selectFrom(Tables.MESSAGE).where(Tables.MESSAGE.ID.in(
create.select(DSL.unnest(..))
Because DSL.unnest is a Table<?>, which makes sense since it is trying to take a List-like object (mostly a literal) and convert it to table.
I have a feeling that I need to find a way to wrap the function around my field name, but I have no clue as to how to proceed.
NOTE. The field message_ids is of type bigint[].
EDIT
So, this is how I am doing it now, and it works exactly as expected, but I am not sure if this is the best way to do it:
Field<Long> unnestMessageIdField = DSL.field(
"unnest(" + SESSION_MESSAGES.MESSAGE_IDS.getName() + ")",
Long.class)
.as("mid");
Field<Long> messageIdField = DSL.field("mid", Long.class);
MESSAGE.ID.in(
ctx.select(messageIdField).from(
ctx.select(unnestMessageIdField)
.from(Tables.CHAT_SESSION_MESSAGES)
.where(Tables.CHAT_SESSION_MESSAGES.SESSION_ID.eq(sessionId))
)
.where(condition)
)
EDIT2
After going through the code on https://github.com/jOOQ/jOOQ/blob/master/jOOQ/src/main/java/org/jooq/impl/DSL.java I guess the right way to do this would be:
DSL.function("unnest", SQLDataTypes.BIGINT.getArrayType(), SESSION_MESSAGES.MESSAGE_IDS)
EDIT3
Since as always lukas is here for my jOOQ woes, I am going to capitalize on this :)
Trying to generalize this function, in a signature of sort
public <T> Field<T> unnest(Field<T[]> arrayField) {
return DSL.function("unnest", <??>, arrayField);
}
I don't know how I can fetch the datatype. There seems to be a way to get DataType<T[]> from DataType<T> using DataType::getArrayDataType(), but the reverse is not possible. There is this class I found ArrayDataType, but it seems to be package-private, so I cannot use it (and even if I could, it does not expose the field elementType).
Old PostgreSQL versions had this funky idea that it is OK to produce a table from within the SELECT clause, and expand it into the "outer" table, as if it were declared in the FROM clause. That is a very obscure PostgreSQL legacy, and this example is a good chance to get rid of it, and use LATERAL instead. Your query is equivalent to this one:
SELECT *
FROM message
WHERE id IN (
SELECT "mid"
FROM session_messages
CROSS JOIN LATERAL unnest(message_ids) AS t("mid")
WHERE session_id = '?'
);
This can be translated to jOOQ much more easily as:
DSL.using(configuration)
.select()
.from(MESSAGE)
.where(MESSAGE.ID).in(
select(field(name("mid"), MESSAGE.ID.getDataType()))
.from(SESSION_MESSAGES)
.crossJoin(lateral(unnest(SESSION_MESSAGES.MESSAGE_IDS)).as("t", "mid"))
.where(SESSION_MESSAGES.SESSION_ID.eq("'?'"))
)
The Edit3 in the question is quite close to a decent solution for this problem.
We can create a custom generic unnest method for jOOQ which accepts Field and use it in jOOQ query normally.
Helper method:
public static <T> Field<T> unnest(Field<T[]> field) {
var type = (Class<T>) field.getType().getComponentType();
return DSL.function("unnest", type, field);
}
Usage:
public void query(SessionId sessionId) {
var field = unnest(SESSION_MESSAGES.MESSAGE_IDS, UUID.class);
dsl.select().from(MESSAGE).where(
MESSAGE.ID.in(
dsl.select(field).from(SESSION_MESSAGES)
.where(SESSION_MESSAGES.SESSION_ID.eq(sessionId.id))
.orderBy(field)
)
);
}
I'm fairly new to lua and have the following problem with an assignment from a class:
We currently extend lua to support objects and inheritance. The Syntax for that is
Class{'MyClass',
attribute1 = String,
attribute2 = Number
}
Class{'MySubClass', MyClass,
attribute3 = Number
}
This works perfectly fine. The real problem lies within the next task: We should support "recursive types", that means a call like
Class{'MyClass', attribute = MyClass}
should result in an class with a field of the same type as the class. When this "class-constructor" is called the variable MyClass is nil, thats why the parameter table doesnt't have an entry attribute. How is it possible to access this attribute?
My first thought was using some kind of nil-table which gets returned every time the global __index is called with an unset key. This nil-table should behave like the normal nil, but can be checked for in the "class-constructor". The problem with this approach are comparisons like nil == unknown. This should return true, but as the __eq meta method of the nil-table is never called we cannot return true.
Is there another approach I'm currently just ignoring? Any hint is greatly appreciated.
Thanks in advance.
Edit:
Here the relevant part of the "testfile". The test by which the code is rated in class is another one and gets published later.
three = 3
print( three == 3 , "Should be true")
print( unknown == nil , "Should be true" )
Class{'AClass', name = String, ref = AClass}
function AClass:write()
print("AClass:write(), name of AClass:", self.name)
end
aclass = AClass:create("A. Class")
aclass:write()
Since MyClass is just a lookup in the global table (_G), you could mess with its metatable's __index to return a newly-defined MyClass object (which you would later need to fill with the details).
However, while feasible, such an implementation is
wildly unsafe, as you could end up with an undefined class (or worse, you may end up inadvertantly creating an infinite lookup loop. Trust me, I've been there)
very hard to debug, as every _G lookup for a non-existing variable will now return a newly created class object instead of nil (this problem could somewhat be reduced by requiring that class names start with an uppercase character)
If you go that route, be sure to also override __newindex.
How about providing the argument in string form?
Class{'MyClass', attribute = 'MyClass'}
Detect strings inside the implementation of Class and process them with _G[string] after creating the class
Or alternatively, use a function to delay the lookup:
Class{'MyClass', attribute = function() return MyClass end}