I am trying to add new column to an existing mnesia table. For that, I use following code.
test()->
Transformer =
fun(X)->
#users{name = X#user.name,
age = X#user.age,
email = X#user.email,
year = 1990}
end,
{atomic, ok} = mnesia:transform_table(user, Transformer,record_info(fields, users),users).
Two records I have
-record(user,{name,age,email}).
-record(users,{name,age,email,year}).
My problem is when I get values from my user table it comes as
{atomic,[{users,sachith,28,sachith#so,1990}]}
Why do I get users record name when I retrieve data from user table?
The table name and the record name are not necessarily the same. You started out with a table called user holding user records, and then you transformed all the user records into users records. So when you read from the table, it will return users records, since that's what the table now contains.
If you look at the internal representation of record,
-record(Name, {Field1,...,FieldN}). is represented by {Name,Value1,...,ValueN}.
So, basically you are converting {user,name,age,email} to {users,name,age,email,year} in your table.
But there is better approach for such migration which will come in handy as you update your records later,
Looking at this production codebase a better snippet for the transformer function,
%%-record(user,{name,age,email}). // old
%%-record(user,{name,age,email,year}). // new
Transformer =
fun(X)->
#user{name = element(2,X),
age = element(3,X),
email = element(4,X),
year = 1990}
end,
I was wondering if there is a way to do the following in a single query?
1) non_populated_models = PropertyPerson.select("property_people.id, count('items.recipient_person_id')").joins(:items).group('items.recipient_person_id, property_people.id')
2) populated_models = PropertyPerson.where(id: [non_populated_models])
Currently, the first group by query only returns the id, and count in the ProperyPerson object. Let's say there were 15 fields in the model and I didn't want to explicitly write them all out. Is there a way I can do this operation in a single query?
The join will work to limit the query to property_people with item and you you will get the extra column as an attr_reader.
people = PropertyPerson.select("property_people.*,
count('items.recipient_person_id') as items_count")
.joins(:items)
.group("property_people.id")
people.first.item_count
I'm using Rails to search through a SQLite table (for other reasons I can't use the standard database-model system) using a SELECT query like so:
info = ActiveRecord::Base.connection.execute("SELECT * FROM #{form_name} WHERE EmailAddress = \"#{user_em}\";")
This returns the correct values, but for some reason the output is in duplicate, the difference being the 2nd set doesn't have column titles in the hash, instead going from 0-[num columns]. For example:
{"id"=>1, "Timestamp"=>"2/27/2017 14:26:03", "EmailAddress"=>"-snip-", 0=>1, 1=>"2/27/2017 14:26:03", 2=>"-snip-"}
(I'll note the obvious- there's only one row in the table with that information in it)
While it's not exactly a fatal problem, I'm interested as to why it's doing so and if it's possible to prevent it. Thanks!
This allows you to read the values both by column index or column name:
id = row[0]
timestamp = row["Timestamp"]
Hi I am trying to query my database by a specific property. Multiple entries in my database may have the same value for the property but I want it to return only the first entry that has that distinct value for the property.
For example, if my domain has a code property, then there might be an entry where "code" = "boy", and there might be another one where "code" = "girl" and there might be yet another one where again "code" = "boy". I want to query it so I get the first entry where "code" = "boy" and the entry where "code" = girl" but not the third entry where code is again equal to boy.
I was able to get the distinct code values from the database using both createCriteria() or namedQueries() but I am not able to get the whole object, just the value of code. How can I get the actual object?
Thinking about I came with an HQL query:
select d
from Domain d
where d.id = (select min(d1.id)
from Domain d1
where d1.code = d.code)
I have the following code:
Dim cn As Object
Dim rs As Object
Dim strSql As String
Dim strConnection As String
Dim AppPath As String
Set cn = CreateObject("ADODB.Connection")
AppPath = Application.ActiveWorkbook.Path
Set rs = CreateObject("ADODB.RecordSet")
strConnection = "Provider=Microsoft.ACE.OLEDB.12.0;" & _
"Data Source=" & AppPath & "\Masterlist_Current_copy.accdb;"
strSql = "SELECT [Neptune Number],[Description],[Manufacturer],[Manufacturer P/N] FROM [All Components];"
cn.Open strConnection
Set rs = cn.Execute(strSql)
'Need Code here to get Info out of recordset
I am trying to get information out of the recordset that has the query result being dumped into it. I'm trying to figure out how to query the recordset and get the number of rows with a specific value in the "Neptune Number" field. I will then insert the correct number of rows into the worksheet I'm modifying. After that I need to get the data for that value and insert it into the worksheet.
Note: I don't care if recordset, datatable or anything else is used I simply need to be able to do what I described above. Please show code.
The easiest way to get where you I think you are asking to go is to modify your SQL statement changing
strSql = "SELECT [Neptune Number],[Description],[Manufacturer],[Manufacturer P/N] FROM [All Components];"
to
strSql = "SELECT [Neptune Number],[Description],[Manufacturer],[Manufacturer P/N] FROM [All Components] WHERE [Neptune Number] = 'Specific Value' ;"
This will force the sql query to only return the records you need. the .find method can be used for filtering the recordset, but i have avoided using it in this instance as it is cleaner to just ask the db for only the information that you want.
to process the recordset you can use the following
with rs
'will skip further processing if no records returned
if not (.bof and .eof) then
'assuming you do not need the headers
'loop through the recordset
do while not .eof
for i = 0 to .fields.count -1
'assuming the active sheet is where you want the data
cells(row, i + colOffset) = .fields(i).value
next
Rows(Row & ":" & Row).Insert
.movenext
loop
end if
end with
Where row is the starting point of your data and colOffset is the starting column of your data. Note that this code does not do things in the exact order you specified in your question (I am inserting rows as needed instead of calcualting the number of records up front.)
I have avoided using .recordcount because I find depending on the database used it will not return a correct record count.