I'm using sqlx library like the following:
type MyData {
Field1 string `json:"db:field1"`
Field2 string `json:"db:field2"`
}
...
res, err := db.Exec("INSERT INTO XXX (field1, field2) VALUES (?, ?)", data.XX, data.XX)
Is it possible to avoid specifying "field1, field2" explicitly, and let sqlx create the query and binding automatically, e.g
db.Exec2("table_name", data)
I didn't find a relevant method to do that.
No. The package sqlx is just a wrapper around the DB driver. It is not an ORM. It expects user-supplied, valid SQL query strings. You may construct the query strings programmatically, and design some method that builds the column names from struct tags using reflect package, but why reinventing the wheel? The advantage of using a lower-level package as sqlx is exactly to maintain your own queries in exchange for not introducing an ORM framework in your codebase. With an ORM instead it is the other way around.
Gorm instead has a set of conventions that do what you want out of the box. You wouldn't even have to specify the db tags:
GORM prefer convention over configuration, by default, GORM uses ID as primary key, pluralize struct name to snake_cases as table name, snake_case as column name, and uses CreatedAt, UpdatedAt to track creating/updating time
type MyData {
Field1 string `json:"field1"`
Field2 string `json:"field2"`
}
data := MyData {
Field1: "foo",
Field2: "bar",
}
result := db.Create(&data)
// results in something like this:
// INSERT INTO my_datas (field1, field2) VALUES ('foo', 'bar')
Related
I'm finding it difficult to define many to many relationship using Gorm in following cases
features(feature_id, name, slug)
operations(operation_id, name, slug)
feature_operations(feature_id, operation_id)
type Feature struct {
FeatureID int64 `gorm:"primaryKey;column:feature_id" json:"feature_id"`
Name string `validate:"required" json:"name"`
Slug string `json:"slug"`
Status string `json:"status"`
Operations []Operation `gorm:"many2many:feature_operations;foreignKey:feature_id"`
appModels.BaseModel
}
When using feature_id, I get error
column feature_operations.feature_feature_id does not exist
When using id, I get error
invalid foreign key: id
Looks like you are not using the convention that gorm suggests where you name your primary key columns just id
so in your case your foreignKey should be the name of the field and you also need to use References to specify column that you want to reference. See the example here:
https://gorm.io/docs/many_to_many.html#Override-Foreign-Key
What you need is this:
type Feature struct {
FeatureID int64 `gorm:"primaryKey;column:feature_id"`
Name string
Slug string
Operations []Operation `gorm:"many2many:feature_operations;foreignKey:FeatureID;References:OperationID"`
}
type Operation struct {
OperationID int64 `gorm:"primaryKey;column:operation_id"`
Name string
Slug string
}
After this the join table will be FEATURE_OPERATIONS with two columns FEATURE_FEATURE_ID AND OPERATION_OPERATION_ID
If you dont like the redundant column names then you need to use the two additional attributes joinForeignKey and joinReferences to choose your own names for the columns like so:
gorm:"many2many:feature_operations;foreignKey:FeatureID;joinForeignKey:FeatureID;References:OperationID;joinReferences:OperationID"
All this extra work is needed because your primary keys are FEATURE_ID and OPERATION_ID instead of just ID
If you can rename the column to follow the convention, you will notice life is much easier with gorm
We are updating our project from v1 to v2.
When we try to update a row by providing only changed fields as a struct, it tries to set created_at column and returns an error. This was working back in v1. According to documentation, during update operations, fields with default values are ignored.
err := r.writeDB.Save(&Record{
Model: Model{
ID: 1,
},
Name: "AB",
}).Error
if err != nil {
return err
}
Generates the following SQL statement
[3.171ms] [rows:0] UPDATE `records` SET `created_at`='0000-00-00 00:00:00',`updated_at`='2020-11-12 15:38:36.285',`name`='AB' WHERE `id` = 1
Returns following error
Error 1292: Incorrect datetime value: '0000-00-00' for column
'created_at' at row 1
With these entities
type Model struct {
ID int `gorm:"primary_key,type:INT;not null;AUTO_INCREMENT"`
CreatedAt time.Time `gorm:"type:TIMESTAMP(6)"`
UpdatedAt time.Time `gorm:"type:TIMESTAMP(6)"`
}
type Record struct {
Model
Name string
Details string
}
There is DB.Omit which allows ignoring a column when executing an update query. But this requires a lot of refactoring in the codebase. Does the behavior changed or is there something missing?
This might help you. Change the structure field (or add to replace default gorm.Model field) like this:
CreatedAt time.Time `gorm:"<-:create"` // allow read and create, but don't update
This tag helps to save created data from update.
In Gorm v2 Save(..) writes all fields to the database. As the CreatedAt field is the zero value, this is written to the database.
For you code to work, you can use a map:
err := r.writeDB.Model(&Record{Model:Model{ID:1}}).Update("name","AB").Error
Another option is to not fill in the Record struct, but just point to the table and use a Where clause:
err := r.writeDB.Model(&Record{}).Where("id = ?", 1).Update("name","AB").Error
If you have multiple updates you can use Updates(...) with a map, see here: https://gorm.io/docs/update.html
I was able to work around this problem using Omit() before save. Like this:
result := r.db.Omit("created_at").Save(item)
It omits the CreatedAt from the resulting update query, and updates everything else.
All examples of working with JSON describe how to serialize to JSON simple or user types (like a struct).
But I have a different case: a) I don't know the fields of my type/object b) every object will have different types.
Here is my case in pseudocode:
while `select * from item` do
while `select fieldname, fieldvalue from fields where fields.itemid = item.id` do
...
For each entity in my database I get field names and field values. In the result I need to get something like this:
{
"item.field1": value,
...
"item.fieldN": value,
"custom_fields": {
"fields.field1": value,
...
"fields.fieldK": value
}
}
What is the best way to do it in Go? Is there any useful libraries or functions in standard library ?
Update: The source of data is the database. In the result i need to get JSON as string to POST it to external web service. So, the program just read data from database and make POST requests to REST service.
What exactly is your target type supposed to be? It can't be a struct since you do not know the fields beforehand.
The only fitting type to me seems to be a map of type map[string]interface{}: with it any nested structure can be achieved:
a := map[string]interface{}{
"item.field1": "val1",
"item.field2": "val2",
"item.fieldN": "valN",
"custom_fields": map[string]interface{}{
"fields.field1": "cval1",
"fields.field2": "cval2",
},
}
b, err := json.Marshal(a)
See playground sample here.
Filling this structure from a database as you hinted at should probably be a custom script (not using json).
Note: custom_fields can also be of other types depending on what type the value column is in the database. If the value column is a string use map[string]string.
I have a model like this:
type Course struct {
Name string `db:"course_name"`
}
type Group struct {
Course *Course
}
type Groups []Group
And when i try to do sqlx.Select for Groups with a query like this:
SELECT c.name as course_name FROM courses as c;
I get
missing destination name course_name in *main.Groups
error.
What is the issue with this code?
You need to use sqlx.Select when you are selecting multiple rows and you want to scan the result into a slice, as is the case for your query, otherwise use sqlx.Get for a single row.
In addition, you can't scan directly into a Group struct because none of its fields are tagged (unlike the Course struct), and the Course field isn't embedded.
Try:
course := Course{}
courses := []Course{}
db.Get(&course, "SELECT name AS course_name FROM courses LIMIT 1")
db.Select(&courses, "SELECT name AS course_name FROM courses")
I changed Course *Course to Course Course - no effect.
When i made it embedded like this:
type Group struct {
Course
}
it worked.
This is also valid:
type Group struct {
*Course
}
Looks like sqlx doesn't understand anything except embedded fields.
Ok, so when you are using an embbeded struct with Sqlx, capitalization is important, at least in my case.
You need to refer to the embedded struct in your sql, like so:
select name as "course.name" from courses...
Notice that course is lower case and the naming involves a dot/period between table and column.
Then your Get or Select should work just fine.
I want to use mongodb as session storage and save a struct based data type into mongodb.
The struct type looks like:
type Session struct {
Id string
Data map[string]interface{}
}
And create reference to Session struct type and put some data into properties like:
type Authen struct {
Name, Email string
}
a := &Authen{Name: "Foo", Email: "foo#example.com"}
s := &Session{}
s.Id = "555555"
s.Data["logged"] = a
How to save the session data s into mongodb and how to query those data back and save into a reference again?
I think the problem can occurs with the data property of type map[string]interface{}.
As driver to mongodb I would use mgo
There's nothing special to be done for inserts. Just insert that session value into the database as usual, and the map type will be properly inserted:
err := collection.Insert(&session)
Assuming the structure described, this will insert the following document into the database:
{id: "555555", data: {logged: {name: "foo", email: "foo#example.com"}}}
You cannot easily query it back like that, though, because the map[string]interface{} does not give the bson package a good hint about what the value type is (it'll end up as a map, instead of Authen). To workaround this, you'd need to implement the bson.Setter interface in the type used by the Data field.