golang - mysql driver - database functions

Question

I have created a struct to store spatial types and I have created a scan function to help query rows in my database. I am having issues inserting this type.

I can insert data using the following sql;

INSERT INTO 'table' ('spot') VALUES (GeomFromText('POINT(10 10)'));

If I use Value interface in database/sql/driver;

type Value interface{}

Value is a value that drivers must be able to handle. It is either nil or an instance of one of these types:

int64

float64

bool

[]byte

string [*] everywhere except from Rows.Next.

time.Time

And use this code;

func (p Point) Value() (driver.Value, error) {
    return "GeomFromText('" + p.ToWKT() + "')", nil
}

I end up with the following sql statement going to the database;

INSERT INTO 'table' ('spot') VALUES ('GeomFromText('POINT(10 10)')');

The issue being that the function GeomFromText is in quotes. Is there a way to avoid this scenario? I am using gorm and trying to keep raw sql queries to a minimum.

The mysql type being used on the database end is a point.

typically the table names and columns would be wrapped in back-ticks or nothing. For instance, a back-tick would be spectacular if the column name was limit or My Column or this-thing — Drew
Have you tried keeping the function call GeomFromText in the query and have your Point Value method return p.ToWKT()? — jmaloney
Thanks for the replies. I suppose I didn't make my difficulties clear. I have no problem with my schema and I know how to insert spatial data, it's more of a sql driver issue. I know that db.Exec("INSERT INTO 'table' ('spot') VALUES (GeomFromText($1))", p.ToWKT()) will work however I am trying to avoid using raw sql queries usch as that. I know that the reason my code is failing is because func (p Point) Value() is returning a string and my MySQL function is being placed in quotes. Is there a way of using this interface and have only part of the string placed in quotes? — devfubar

Drew Drew · Accepted Answer · 2015-12-11T23:48:28

Please see the two urls below where the concept was poached from

Schema

-- http://howto-use-mysql-spatial-ext.blogspot.com/

create table Points
(   id int auto_increment primary key,
    name VARCHAR(20) not null, 
    location Point NOT NULL, 
    description VARCHAR(200) not null, 
    SPATIAL INDEX(location),
    key(name)
)engine=MyISAM; -- for use of spatial indexes and avoiding error 1464

-- insert a row, so we can prove Update later will work
INSERT INTO Points (name, location, description) VALUES 
( 'point1' , GeomFromText( ' POINT(31.5 42.2) ' ) , 'some place');

Update statement

-- concept borrowed from http://stackoverflow.com/a/7135890
UPDATE Points 
set location = PointFromText(CONCAT('POINT(',13.33,' ',26.48,')'))
where id=1;

Verify

select * from points;

(when you open the Value Editor to see the blob, the point is updated)

So, the takeaway is to play with the concat() inside of the update statement.

golang - mysql driver - database functions

1 Answers

Schema

Update statement

Verify