I am trying to write a function to query all results that match a set of conditions and save them in a struct slice.
// Queries the database for the given set of fields and some string conditions specified as a map
func QueryAllRecords(db *gorm.DB, outputObject interface{}, conditions map[string]interface{}) {
result := db.Where(conditions).Find(&outputObject)
if result.Error != nil {
panic(result.Error)
}
log.Println(Utils.CreateLogMessage("Queried all records", outputObject))
}
According to the GORM docs (https://gorm.io/docs/query.html#Retrieving-all-objects), I can query all records using the .Find() function and then specify the struct where the output of the query will be saved.
This is where I make my function call to QueryAllRecords:
var outputObject []Models.Product
conditions := map[string]interface{}{"name": "Sample Product"}
DB.QueryAllRecords(db, outputObject, conditions)
fmt.Println(outputObject)
When I try to print outputObject, I get an empty an empty slice []. It seems like the .Find(&outputObject) is not saving the result in the slice like I want it to. I can successfully print outputObject within the function itself, but not after it has returned.
Use the DB.QueryAllRecords(db, outputObject, conditions) instead
Related
I am using https://github.com/labstack/echo in one of the projects. I am using c.QueryParam to parse the query parameter and its values. One of the values contains a + symbol in it and it converts them to a space character (which is correct). However, I would like to retain the + character in the value.
Ex: http://localhost:8080?param=test+test
fmt.Println(c.QueryParam("param"))
Right now it outputs test test. However, I am expecting the output as test+test. Is it possible to achieve it using c.QueryParam?
You can get the raw query and then parse the parameter and it's value
func hello(c echo.Context) error {
//to get the raw query
fmt.Println(c.Request().URL.RawQuery)
return c.String(http.StatusOK, "Hello, World!")
}
Then you can use strings.split(rawQuery,"=") to get the parameter and it's value.
You can write a custom helper function like below -
func CustomQueryParam(c echo.Context, name string) string {
qParams := make(map[string]string)
for _, singleQueryParamStr := range strings.Split(c.QueryString(), "&") {
val := strings.Split(singleQueryParamStr, "=")
qParams[val[0]] = val[1]
}
return qParams[name]
}
func TestGet(c echo.Context) error {
param := CustomQueryParam(c, "param")
fmt.Println(param)
return c.JSON(http.StatusOK, map[string]interface{}{
"message": "request is successful",
})
}
Now, the output is as your expection. It prints test+test. But what actually CustomQueryParam do?
Okay, let's explore the insight. Suppose, the api call is -
http://localhost:8080?param=test1+test2¶m2=test3
The CustomQueryParam function will take an echo.Context instance and the query param name as function parameters.
Then, inside for loop the whole query string i.e. in our case which is param=test1+test2¶m2=test3 is split by & and stored into string slice made by each query param string ([]string{"param=test1+test2", "param2=test3"}).
After that, we iterate over each query param string and again split into a string slice of two values having first value as param name and second value as param value. For example, for first query param string, the resultant output is like below -
"param=test1+test2" => []string{"param", "test1+test2"}
Then, the first value (param name) is assigned as map key and second value (param value) as map value.
After finishing above process for every query string, the map value by query param name (which is the parameter of this function) is returned.
One of the interesting fact about this custom function is that it returns empty string if query param is not found.
I am developing an API using Go which connects to MySQL database for some query execution. Am using GORM for database operations. But am stuck at printing the SELECT query output for the tables which I don't have the column names.
My use case is that, I need to run the query on multiple tables where I don't have an idea about what their column names and types are. And so I cannot pre-define a struct for all the current and future tables which might get added.
Is there a way to print/save the SELECT query output without a pre-defined struct ?
I tried do some using empty struct but it didn't help me.
P.S: Am a beginner in Go
type Testing struct{}
var test Testing
dsn := fmt.Sprintf("%v:%v#tcp(%v:%v)/%v", myds.DBuser, myds.DBpassword, myds.DBhost, myds.DBport, myds.DBname)
db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
if err != nil {
fmt.Println(err)
}
tx := db.Raw(query).Scan(&test)
if tx.Error != nil {
fmt.Println(tx.Error)
}
fmt.Println(test)
You can use an anonymous struct
Let's say you have a struct:
type User struct{
FirstName string
LastName string
}
Query:
SELECT CONCAT(first_name,last_name) AS full_name from users;
Notice the new column full_name
you can simply do
var fullName = struct{FullName string}{}
Notice how I use pascal case & FullName has to be the field name
A capital letter in between will represent a _
Field is public so it can be accessed outside.
full_name(query) = FullName(field)
pass this fullName object as a bucket to your Scan and it should work.
db.Raw(query).Scan(&fullName)
EDIT:
Your query will have some result right?
Let me assume that you have
column_one,column_two... column_n
Now, to get the data from all the columns or selected ones if you want, you simply have to define fields (in anonymous struct) with specific names. In our case:
struct{ColumnOne,ColumnTwo,..ColumnN interface{}}{}
P.S. I have used interface{}, you can use types depending on the data your column returns.
It worked for me by using a map type with interface. This helped me to save the SELECT query results without pre-defined struct or the column names.
dsn := fmt.Sprintf("%v:%v#tcp(%v:%v)/%v", myds.DBuser, myds.DBpassword, myds.DBhost, myds.DBport, myds.DBname)
db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
if err != nil {
fmt.Println(err)
}
var result []map[string]interface{}
tx := db.Raw(query).Scan(&result)
if tx.Error != nil {
fmt.Println(tx.Error)
return
}
bytes, _ := json.Marshal(result)
fmt.Println(string(bytes))
I'm working on a golang application in which I need to fetch last record from the table so I'm not able to do it. I have models mention below:-
type SQLTransaction struct {
Id int `protobuf:"bytes,1,opt,name=id,proto3" json:"id,omitempty"`
Version uint64 `protobuf:"varint,1,opt,name=version,proto3" json:"version,omitempty" gorm:"primaryKey"`
Hash string `protobuf:"bytes,3,opt,name=hash,proto3" json:"hash,omitempty"`
VmStatusId int `protobuf:"bytes,6,opt,name=vm_status_id,proto3" json:"vm_status_id,omitempty"`
}
Here is my gorm function in which I want to fetch the last record
func (mgr *manager) GetLastTxn() (int, error) {
var versionId int
resp := mgr.connection.Table("transactions").Last("", "version")
return versionId, resp.Error
}
Error:-
model value required
[0.053ms] [rows:0] SELECT * FROM `transactions` WHERE version ORDER BY `transactions`. DESC LIMIT 1
0 model value required
How can I achieve it please any help. Thanks in advance.
There are a couple of issues in your example that should be handled.
First, the error model value required suggests that the Last method needs a model to store the result. If you want the entire record with all the data you can do it like this:
var lastVersion SQLTransaction
resp := mgr.connection.Table("transactions").Last(&lastVersion)
If you only want the ID of the record, you do something like this:
var lastVersion struct {
ID int
}
resp := mgr.connection.Table("transactions").Last(&lastVersion)
Next, you don't need Last("", "version") because it doesn't do what you think it does. The first parameter is a pointer to your resulting object (which for all go-gorm methods always should be an object or a slice). The second one is a condition for the WHERE clause. So the correct syntax, if you don't need an additional WHERE clause, is:
resp := mgr.connection.Table("transactions").Last(&lastVersion)
If you look at the code of the Last method, it considers the primary key when it executes the method, so you don't even need any additional parameters or conditions.
first of all: I am totally newbie in golang, so I may not understand well.
I am tasked to write a Go data extractor from one database using "gorp". The problem is with one table, that has custom field "TimeRange".
It is defined as:
type TimeRange struct {
From string
To string
}
Sadly when I try to fetch row I am getting scanner error, so I realised I need a custom scanner.
// Scan - Implement the database/sql scanner interface
func (tr *TimeRange) Scan(value interface{}) error {
tr.From = "mis"
tr.To = "lala"
fmt.Printf("%v\n", *tr)
return nil
}
So I expect to see fixed '{mis lala}' in returned string.
Why I am getting:
var q2 []models.Dashboard
result, err := dbmap.Select(&q2, "select * from dashboard where id=3")
fmt.Printf("q2=%v\n", q2)
prints:
p2=[{{<nil> Tomek b1f6f0ba-f618-00d6-6d24-8410a9219c95}}]
which is:
TimeRange, UserName and UUID
Might be important: using "gorp" for DB managment
the scan function would be called on passed value type to dbmap.Select() so in your case, you need to implement Dashboard as scanner.
I'm writing code that allows data access from a database. However, I find myself repeating the same code for similar types and fields. How can I write generic functions for the same?
e.g. what I want to achieve ...
type Person{FirstName string}
type Company{Industry string}
getItems(typ string, field string, val string) ([]interface{}) {
...
}
var persons []Person
persons = getItems("Person", "FirstName", "John")
var companies []Company
cs = getItems("Company", "Industry", "Software")
So you're definitely on the right track with the idea of returning a slice of nil interface types. However, you're going to run into problems when you try accessing specific members or calling specific methods, because you're not going to know what type you're looking for. This is where type assertions are going to come in very handy. To extend your code a bit:
getPerson(typ string, field string, val string) []Person {
slice := getItems(typ, field, val)
output := make([]Person, 0)
i := 0
for _, item := range slice {
// Type assertion!
thing, ok := item.(Person)
if ok {
output = append(output, thing)
i++
}
}
return output
}
So what that does is it performs a generic search, and then weeds out only those items which are of the correct type. Specifically, the type assertion:
thing, ok := item.(Person)
checks to see if the variable item is of type Person, and if it is, it returns the value and true, otherwise it returns nil and false (thus checking ok tells us if the assertion succeeded).
You can actually, if you want, take this a step further, and define the getItems() function in terms of another boolean function. Basically the idea would be to have getItems() run the function pass it on each element in the database and only add that element to the results if running the function on the element returns true:
getItem(critera func(interface{})bool) []interface{} {
output := make([]interface{}, 0)
foreach _, item := range database {
if criteria(item) {
output = append(output, item)
}
}
}
(honestly, if it were me, I'd do a hybrid of the two which accepts a criteria function but also accepts the field and value strings)
joshlf13 has a great answer. I'd expand a little on it though to maintain some additional type safety. instead of a critera function I would use a collector function.
// typed output array no interfaces
output := []string{}
// collector that populates our output array as needed
func collect(i interface{}) {
// The only non typesafe part of the program is limited to this function
if val, ok := i.(string); ok {
output = append(output, val)
}
}
// getItem uses the collector
func getItem(collect func(interface{})) {
foreach _, item := range database {
collect(item)
}
}
getItem(collect) // perform our get and populate the output array from above.
This has the benefit of not requiring you to loop through your interface{} slice after a call to getItems and do yet another cast.