i have quite large application with complex DB structure (lots of tables with foregin keys.. ).
This application exists in 2 instances ( so there are 2 schema-identical DB's ), every has different data (some data can be same like 'district').
I need to create third application for reading data only. This third application needs to read data from both databases, merging them and displaying them.
I need to by able to use existing application code for reading, sorting, filtering, paginating.
What is most effective way to achieve this in cakephp?
Thanks in advance
Possible solution:
- create your own data source ( extend existing Mysql )
- overload "read" method, in this overloaded method, merge records and return
Related
I am working on a project to create a simplified version of SQLite Database. I got stuck when trying to figure out how does it manages to store data of multiple tables with different schema, in a single file. I suppose it should be using some indexes to map the data of different tables. Can someone shed more light on how its actually done? Thanks.
Edit: I suppose there is already an explanation in the docs, but looking for some easier way to understand it better and faster.
The schema is the list of all entities (tables, views etc) (the database as a whole) rather than a database existing of many schemas on a per entity basis.
Data itself is stored in pages each page being owned by an entity. It is these blocks that are saved.
The default page size is 4k. You will notice that the file size will always be a mutliple of 4K. You could also, with experimentation create a database with some tables, note it's size, then add some data, and if the added data does not require another page, see that the size of the file is the same. This demonstrating how it's all about pages rather than a linear/contiguos stream of data.
It, the schema, is saved in a table called sqlite_master. This table has columns :-
type (the type e.g. table etc),
name (the name given to the entity),
tbl_name (the tale to which the entity applies )
root page (the map to the first page)
sql (the SQL used to generate the entity, if any)
note that another schema, sqlite_temp_master, may also exist if there are temporary tables.
For example :-
Using SELECT * FROM sqlite_master; could result in something like :-
2.6. Storage Of The SQL Database Schema
We came across a situation where we need to compare the data between two databases and both databases have different architecture ( new and old - means table names and field names on one database is different than other ) .
We cannot use any third party tool .Also the data is in huge volume so Excel would not be the good option.
Need help ...
Thanks
The setup
I have the following database setup:
CentralDB
Table: Stores
Table: Users
Store1DB
Table: Orders
Store2DB
Table: Orders
Store3DB
Table: Orders
Store4DB
Table: Orders
... etc
CentralDB contains the users, logging and a Stores table with the name of each store database and general information about each store such as address, name, description, image, etc...
All the StoreDB's use the same structure just different data.
It is important to know that the list of stores will shrink and increase in the future.
The main client communicating with this setup is an API REST Service which gets passed a STOREID in the Header of each request telling it which database to connect to. This works flawlessly so far.
The reasoning
Whenever we need to do database maintenance on one store, we don't want all other stores to be down.
Backup management should be per store
Not having to write the WHERE storeID=x every time and for every table
Performance: each store could run on its own database server if the need arises
The goal
I need my REST API Service to somehow get all orders from all stores in one query.
Will you help me figure out a way to do this without hardcoding all storedb names? I was thinking about a stored procedure on the CentralDB but I was hoping there would be other solutions. In any case it has to be very efficient.
One option would be to have a list of databases stored in a "system" table in CentralDB.
Then you could create a stored procedure that would read the database names from the table, loop through them with cursor and generate a dynamic SQL that would UNION the results from all the databases. This way you would get a single recordset of results.
However, this database design is IMHO flawed. There is no reason for using multiple databases to store data that belongs to the same "domain". All the reasons that you have mentioned can be solved by using a single database with proper database design. Having multiple databases will create multiple problems on the long term:
you will need to change structure of all the DBs when you modify your database model
you will need to create/drop new databases when new stores are added/removed from your system
you will need to have items and other entities that are "common" to all the stores duplicated in all the DBs
what about reporting requirements (e.g. get sales data for stores 1 and 2 together, etc.) - this will require creating complex union queries...
etc...
On the long term, managing and maintaining this model will be a big pain.
I'd maintain a set of views that UNION ALL all the data. Every time a store is added or deleted those views must be updated. This can be automated.
The views provide an illusion to the application that there is only one database.
What I would not do is have each SQL query or procedure query all the database names and create dynamic SQL. That would entail lots of code duplication and an unnecessary loss of performance. This approach is error prone. Better generate code once in a central place and have all other SQL code reference that generated code.
I'm working on a data conversion utility which can push data from one master database out to a number of different databases. The utility its self will have no knowledge of how data is kept in the destination (table structure), but I would like to provide writing a SQL statement to return data from the destination using a complex SQL query with multiple join statements. As long as the data is in a standardized format that the utility can recognize (field names) in an ADO query.
What I would like to do is then modify the live data in this ADO Query. However, since there are multiple join statements, I'm not sure if it's possible to do this. I know at least with BDE (I've never used BDE), it was very strict and you had to return all fields (*) and such. ADO I know is more flexible, but I don't know quite how flexible in this case.
Is it supposed to be possible to modify data in a TADOQuery in this manner, when the results include fields from different tables? And even if so, suppose I want to append a new record to the end (TADOQuery.Append). Would it append to two different tables?
The actual primary table I'm selecting from has a complimentary table which is joined by the same primary key field, one is a "Small" table (brief info) and the other is a "Detail" table (more info for each record in Small table). So, a typical statement would include something like this:
select ts.record_uid, ts.SomeField, td.SomeOtherField from table_small ts
join table_detail td on td.record_uid = ts.record_uid
There are also a number of other joins to records in other tables, but I'm not worried about appending to those ones. I'm only worried about appending to the "Small" and "Detail" tables - at the same time.
Is such a thing possible in an ADO Query? I'm willing to tweak and modify the SQL statement in any way necessary to make this possible. I have a bad feeling though that it's not possible.
Compatibility:
SQL Server 2000 through 2008 R2
Delphi XE2
Editing these Fields which have no influence on the joins is usually no problem.
Appending is ... you can limit the Append to one of the Tables by
procedure TForm.ADSBeforePost(DataSet: TDataSet);
begin
inherited;
TCustomADODataSet(DataSet).Properties['Unique Table'].Value := 'table_small';
end;
but without an Requery you won't get much further.
The better way will be setting Values by Procedure e.g. in BeforePost, Requery and Abort.
If your View would be persistent you would be able to use INSTEAD OF Triggers
Jerry,
I encountered the same problem on FireBird, and from experience I can tell you that it can be made(up to a small complexity) by using CachedUpdates . A very good resource is this one - http://podgoretsky.com/ftp/Docs/Delphi/D5/dg/11_cache.html. This article has the answers to all your questions.
I have abandoned the original idea of live ADO query updates, as it has become more complex than I can wrap my head around. The scope of the data push project has changed, and therefore this is no longer an issue for me, however still an interesting subject to know.
The new structure of the application consists of attaching multiple "Field Links" on various fields from the original set of data. Each of these links references the original field name and a SQL Statement which is to be executed when that field is being imported. Multiple field links can be on one single field, therefore can execute multiple statements, placing the value in various tables, etc. The end goal was an app which I can easily and repeatedly export a common dataset from an original source to any outside source with different data structures, without having to recompile the app.
However the concept of cached updates was not appealing to me, simply for the fact pointed out in the link in RBA's answer that data can be changed in the database in the mean-time. So I will instead integrate my own method of customizable data pushes.
I have a database table and I want to load it to model? Not by specified condition but whole table. How to do it?
models in ATK4 are used to represent data and to abstract the underlying technicalities but not directly hold them.
it is used by MVCGrid, MVCForm and CRUD to know how data is to be presented / laid out to the user's interface.
though models may not hold data, they are used to retrieve it through dsql.
example:
$m = $this->add('Model_UserAccess');
$u = $m->dsql()
->field('usernm')
->field('acclvl')
//->do_getOne(); // return only 1 record
->do_getAll(); // return all records
the use of DSQL or Dynamic SQL is important
to retrieve data from tables and save it back.
I have a very simple script that creates the necessary .php files to copy to /lib/Model.
I did it because was migrating an Access application with tables of 20-30 attributes and was very tedious to create it by hand.
The script it's very very basic, but it's very useful for me.
Here is the link
https://github.com/ajmmartinez/atk4_create_mod
Try
$data = $mymodel->getRows();
This will get all the data from the model and store into the array. Your question is difficult to understand, so I'm not sure how to reply.