I am developing a simple Hyperledger Fabric Wallet type application in Java chaincode with basically 2 models: Wallet and MoneyTransfer. MoneyTransfer has the data, amount and ids for "fromWallet" and "targetWallet".
I have not found examples of how to do a query in the ChaincodeStub to fetch, for example, all MoneyTransfer's for a specific walletId. Is this possible or models can only be fetched by id?
Any URL for doc or help on how to do this? (Samples I have found just fetch models by Id but don't perform queries based on specific properties in the models) Thanks.
Using CouchDB as the state database you should be able to write JSON objects into the state database and run "rich" queries against a particular property in the JSON object. There are samples for doing this in Javascript and in Go, but I don't know if there are any for Java.
These docs give the background:
https://hyperledger-fabric.readthedocs.io/en/latest/couchdb_tutorial.html
https://hyperledger-fabric.readthedocs.io/en/latest/couchdb_as_state_database.html
My requirement is like, i have a json file data as below.,
{Key1: value1, key2: value 2,....} with file name example.json
It should be inserted into sql server as,
Take name: example
Data as below,
Id key1 key2
1 value 1 value 2
I'm searching for a solution such that, there won't be any Java layer complexities, like first converting this data into Java beans then inserting into sql using java database drivers...
Implementation should be language and database independent. In future if i change my database server, then it should be a minimal change.
The coupling should be very loose. Like if i introduce a new key in JSON file, that should be minimal change in the solution.
Tia
So, use some library that can do http request to the server. For eg, if you want insert your json data to server in android app , then use simple libraries like Volley , OkHttp etc.
Problem with your question is , we dont know which server you r using and what application you are doing,, and which programming language you wanna use,, So, im assuming is java android,,
I wish to display some data from my SQL server into my application.
Let me explain throw an example what have i done until now, and please tell me how should i go on with my work:
(1) I have a database named: 'DB1'
(2) In my database i have table named 'users':
Id, Name, LastName
1 Dave Stone
2 Rose Mary
3 Gray Lone
(3) I created 3 php files: 1/ config.php (sets up my database log in information like password...)
2/ DBConnection.php : `
// Connecting to database
public function connect() {
require_once 'Config.php';
// Connecting to mysql database
$this->conn = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_DATABASE);
// return database handler
return $this->conn;
}
}
?>
3/ GetUsers.php which i dont know how should i write it - this would be the code which will echo whatever i want from the table.
(4) Inside my android studio project i have a MainActivity.java and i want to get all the LastNames of all the users in the database and do whatever with them... like print them into a text box it doesn't really matter (let's say i don't know how many users I have).
I need some one to help me get stages (3)3/ + (4) done / explained.
I think what you mean is a good method to retrieve and set values from app to database, the best and most prominent way is using basic REST services that convert your db values to JSON then you load the json using your api key as authentication, it might sound really stressful but is in fact very easy and flexible to implement, the only way you can directly set and get db values on android is using sqlite (android local inbuilt db)
The best tutorial and major explanation for exactly what you want to achieve is here
http://www.androidhive.info/2014/01/how-to-create-rest-api-for-android-app-using-php-slim-and-mysql-day-12-2/
Then this one for further works
http://www.androidhive.info/2012/01/android-login-and-registration-with-php-mysql-and-sqlite/
It covers how you make a rest service yourself
I created python script that sends notifications when result declared but I want to make website that takes data of student email id and store in database.
Now here problem is that I don't know django framework so it takes time to make website.
Java, database connection, Data insertion,
Servelet calling easily do that by me.
Want to know way that java html css takes input from user and stores in database and then python program retrieves that data.
Hope you understand my question.
If you know python, I think Django might be a good choice for you. Django itself attempts to support as many features as possible on the backend. You only need to configure the database parameters in settings.py and Django ORM can automate the transfer of data stored in tables into objects. You don't have to implement the features yourself and it saves you tons of time.
Django has its own ModelForm class. It maps to the Models(eg. Student), it is quite easy to submit your Student info and store it in db.
# settings.py
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.mysql',
'OPTIONS': {
'read_default_file': '/path/to/my.cnf',
},
}
}
# my.cnf
[client]
database = NAME
user = USER
password = PASSWORD
default-character-set = utf8
If you insist using Java to implement the database backend, for sure you can share it with python. Some choices like JDBC, Hibernate and Mybatis.
Yes you can share the DB, you'll have to install the corresponding dependencies for connecting python to the DB as well as for Java. I've done this with postgresql, mysql and mssql
I want to build an SQL string to do database manipulation (updates, deletes, inserts, selects, that sort of thing) - instead of the awful string concat method using millions of "+"'s and quotes which is unreadable at best - there must be a better way.
I did think of using MessageFormat - but its supposed to be used for user messages, although I think it would do a reasonable job - but I guess there should be something more aligned to SQL type operations in the java sql libraries.
Would Groovy be any good?
First of all consider using query parameters in prepared statements:
PreparedStatement stm = c.prepareStatement("UPDATE user_table SET name=? WHERE id=?");
stm.setString(1, "the name");
stm.setInt(2, 345);
stm.executeUpdate();
The other thing that can be done is to keep all queries in properties file. For example
in a queries.properties file can place the above query:
update_query=UPDATE user_table SET name=? WHERE id=?
Then with the help of a simple utility class:
public class Queries {
private static final String propFileName = "queries.properties";
private static Properties props;
public static Properties getQueries() throws SQLException {
InputStream is =
Queries.class.getResourceAsStream("/" + propFileName);
if (is == null){
throw new SQLException("Unable to load property file: " + propFileName);
}
//singleton
if(props == null){
props = new Properties();
try {
props.load(is);
} catch (IOException e) {
throw new SQLException("Unable to load property file: " + propFileName + "\n" + e.getMessage());
}
}
return props;
}
public static String getQuery(String query) throws SQLException{
return getQueries().getProperty(query);
}
}
you might use your queries as follows:
PreparedStatement stm = c.prepareStatement(Queries.getQuery("update_query"));
This is a rather simple solution, but works well.
For arbitrary SQL, use jOOQ. jOOQ currently supports SELECT, INSERT, UPDATE, DELETE, TRUNCATE, and MERGE. You can create SQL like this:
String sql1 = DSL.using(SQLDialect.MYSQL)
.select(A, B, C)
.from(MY_TABLE)
.where(A.equal(5))
.and(B.greaterThan(8))
.getSQL();
String sql2 = DSL.using(SQLDialect.MYSQL)
.insertInto(MY_TABLE)
.values(A, 1)
.values(B, 2)
.getSQL();
String sql3 = DSL.using(SQLDialect.MYSQL)
.update(MY_TABLE)
.set(A, 1)
.set(B, 2)
.where(C.greaterThan(5))
.getSQL();
Instead of obtaining the SQL string, you could also just execute it, using jOOQ. See
http://www.jooq.org
(Disclaimer: I work for the company behind jOOQ)
One technology you should consider is SQLJ - a way to embed SQL statements directly in Java. As a simple example, you might have the following in a file called TestQueries.sqlj:
public class TestQueries
{
public String getUsername(int id)
{
String username;
#sql
{
select username into :username
from users
where pkey = :id
};
return username;
}
}
There is an additional precompile step which takes your .sqlj files and translates them into pure Java - in short, it looks for the special blocks delimited with
#sql
{
...
}
and turns them into JDBC calls. There are several key benefits to using SQLJ:
completely abstracts away the JDBC layer - programmers only need to think about Java and SQL
the translator can be made to check your queries for syntax etc. against the database at compile time
ability to directly bind Java variables in queries using the ":" prefix
There are implementations of the translator around for most of the major database vendors, so you should be able to find everything you need easily.
I am wondering if you are after something like Squiggle (GitHub). Also something very useful is jDBI. It won't help you with the queries though.
I would have a look at Spring JDBC. I use it whenever I need to execute SQLs programatically. Example:
int countOfActorsNamedJoe
= jdbcTemplate.queryForInt("select count(0) from t_actors where first_name = ?", new Object[]{"Joe"});
It's really great for any kind of sql execution, especially querying; it will help you map resultsets to objects, without adding the complexity of a complete ORM.
I tend to use Spring's Named JDBC Parameters so I can write a standard string like "select * from blah where colX=':someValue'"; I think that's pretty readable.
An alternative would be to supply the string in a separate .sql file and read the contents in using a utility method.
Oh, also worth having a look at Squill: https://squill.dev.java.net/docs/tutorial.html
I second the recommendations for using an ORM like Hibernate. However, there are certainly situations where that doesn't work, so I'll take this opportunity to tout some stuff that i've helped to write: SqlBuilder is a java library for dynamically building sql statements using the "builder" style. it's fairly powerful and fairly flexible.
I have been working on a Java servlet application that needs to construct very dynamic SQL statements for adhoc reporting purposes. The basic function of the app is to feed a bunch of named HTTP request parameters into a pre-coded query, and generate a nicely formatted table of output. I used Spring MVC and the dependency injection framework to store all of my SQL queries in XML files and load them into the reporting application, along with the table formatting information. Eventually, the reporting requirements became more complicated than the capabilities of the existing parameter mapping frameworks and I had to write my own. It was an interesting exercise in development and produced a framework for parameter mapping much more robust than anything else I could find.
The new parameter mappings looked as such:
select app.name as "App",
${optional(" app.owner as "Owner", "):showOwner}
sv.name as "Server", sum(act.trans_ct) as "Trans"
from activity_records act, servers sv, applications app
where act.server_id = sv.id
and act.app_id = app.id
and sv.id = ${integer(0,50):serverId}
and app.id in ${integerList(50):appId}
group by app.name, ${optional(" app.owner, "):showOwner} sv.name
order by app.name, sv.name
The beauty of the resulting framework was that it could process HTTP request parameters directly into the query with proper type checking and limit checking. No extra mappings required for input validation. In the example query above, the parameter named serverId
would be checked to make sure it could cast to an integer and was in the range of 0-50. The parameter appId would be processed as an array of integers, with a length limit of 50. If the field showOwner is present and set to "true", the bits of SQL in the quotes will be added to the generated query for the optional field mappings. field Several more parameter type mappings are available including optional segments of SQL with further parameter mappings. It allows for as complex of a query mapping as the developer can come up with. It even has controls in the report configuration to determine whether a given query will have the final mappings via a PreparedStatement or simply ran as a pre-built query.
For the sample Http request values:
showOwner: true
serverId: 20
appId: 1,2,3,5,7,11,13
It would produce the following SQL:
select app.name as "App",
app.owner as "Owner",
sv.name as "Server", sum(act.trans_ct) as "Trans"
from activity_records act, servers sv, applications app
where act.server_id = sv.id
and act.app_id = app.id
and sv.id = 20
and app.id in (1,2,3,5,7,11,13)
group by app.name, app.owner, sv.name
order by app.name, sv.name
I really think that Spring or Hibernate or one of those frameworks should offer a more robust mapping mechanism that verifies types, allows for complex data types like arrays and other such features. I wrote my engine for only my purposes, it isn't quite read for general release. It only works with Oracle queries at the moment and all of the code belongs to a big corporation. Someday I may take my ideas and build a new open source framework, but I'm hoping one of the existing big players will take up the challenge.
Why do you want to generate all the sql by hand? Have you looked at an ORM like Hibernate Depending on your project it will probably do at least 95% of what you need, do it in a cleaner way then raw SQL, and if you need to get the last bit of performance you can create the SQL queries that need to be hand tuned.
You can also have a look at MyBatis (www.mybatis.org) . It helps you write SQL statements outside your java code and maps the sql results into your java objects among other things.
Google provides a library called the Room Persitence Library which provides a very clean way of writing SQL for Android Apps, basically an abstraction layer over underlying SQLite Database. Bellow is short code snippet from the official website:
#Dao
public interface UserDao {
#Query("SELECT * FROM user")
List<User> getAll();
#Query("SELECT * FROM user WHERE uid IN (:userIds)")
List<User> loadAllByIds(int[] userIds);
#Query("SELECT * FROM user WHERE first_name LIKE :first AND "
+ "last_name LIKE :last LIMIT 1")
User findByName(String first, String last);
#Insert
void insertAll(User... users);
#Delete
void delete(User user);
}
There are more examples and better documentation in the official docs for the library.
There is also one called MentaBean which is a Java ORM. It has nice features and seems to be pretty simple way of writing SQL.
Read an XML file.
You can read it from an XML file. Its easy to maintain and work with.
There are standard STaX, DOM, SAX parsers available out there to make it few lines of code in java.
Do more with attributes
You can have some semantic information with attributes on the tag to help do more with the SQL. This can be the method name or query type or anything that helps you code less.
Maintaince
You can put the xml outside the jar and easily maintain it. Same benefits as a properties file.
Conversion
XML is extensible and easily convertible to other formats.
Use Case
Metamug uses xml to configure REST resource files with sql.
If you put the SQL strings in a properties file and then read that in you can keep the SQL strings in a plain text file.
That doesn't solve the SQL type issues, but at least it makes copying&pasting from TOAD or sqlplus much easier.
How do you get string concatenation, aside from long SQL strings in PreparedStatements (that you could easily provide in a text file and load as a resource anyway) that you break over several lines?
You aren't creating SQL strings directly are you? That's the biggest no-no in programming. Please use PreparedStatements, and supply the data as parameters. It reduces the chance of SQL Injection vastly.