The new flexible environment datastore interface does not seem to support IN operation when running a query. I hope that I'm wrong, and if so, how can one use an IN operator in the new Java interface of Datastore?
A query like - WHERE color IN('RED', 'BLACK'), it is not supported by the Datastore (server side). Same is the case with OR operator (e.g. WHERE color='RED' OR color='BLACK'). Some client APIs have added this functionality by splitting the query into multiple and then merging the results from each query. The new google-cloud-java API does not support this yet. For now, you would have to run multiple queries for each value in the IN clause and merge the results.
Here’s an example from the documentation:
If you want to set more than one filter on a query, you must use CompositeFilter, which requires at least two filters.
Filter tooShortFilter = new FilterPredicate("height", FilterOperator.LESS_THAN, minHeight);
Filter tooTallFilter = new FilterPredicate("height", FilterOperator.GREATER_THAN, maxHeight);
Filter heightOutOfRangeFilter = CompositeFilterOperator.or(tooShortFilter, tooTallFilter);
Query q = new Query("Person").setFilter(heightOutOfRangeFilter);
You can also use .and(). The code here is for Java 7. For Java 8 you can find a corresponding code in the documentation referenced above. I hope that helps.
Now to IN. While I have not tried it myself recently, the current documentation states that it can still be used as an operator. According to it, something like the code below should work:
Filter propertyFilter = new FilterPredicate("height", FilterOperator.IN, minHeights);
Query q = new Query("Person").setFilter(propertyFilter);
Alternatively, you could use Google GQL. It will allow you to write SQL-like syntax, in which you can use in(...).
I tried using the repository query methods, but I got an error informing that it is not supported.
Only solved for me using the #Query annotation;
Example:
#Query("select * from UserGroup where name IN #names")
List<Company> findAllByName(List<String> names);
I have just started learning Couchbase. I am trying to write a basic query using java sdk but I am not able to understand how to write it. Below is the query:
SELECT *
FROM users_with_orders usr
JOIN orders_with_users orders
ON KEYS ARRAY s.order_id FOR s IN usr.shipped_order_history END
This is for joining without array:
LetPath path = select("*,META(usr).id as _ID,META(usr).cas as _CAS).from(bucketName +" usr").join(bucketname +" orders").onKeys("usr.order_id)
How should I proceed with the above query for on keys array?
Thanks!!!!
As described in the docs on Querying from the SDK, you can use either a simple string with the Java SDK or use the DSL. For example:
// query with a simple string
System.out.println("Simple string query:");
N1qlQuery airlineQuery = N1qlQuery.simple("SELECT `travel-sample`.* FROM `travel-sample` WHERE name=\"United Airlines\" AND type=\"airline\"");
N1qlQueryResult queryResult = bucket.query(airlineQuery);
for (N1qlQueryRow result: queryResult) {
System.out.println(result.value());
}
//query with a parameter using the DSL
System.out.println("Parameterized query using the DSL:");
Statement statement = select(path(i("travel-sample"), "*")).from(i("travel-sample")).where(x("name").eq(x("$airline_param")).and(x("type").eq(s("airline"))));
JsonObject placeholderValues = JsonObject.create().put("airline_param", "United Airlines");
N1qlQuery airlineQueryParameterized = N1qlQuery.parameterized(statement, placeholderValues);
N1qlQueryResult queryResultParameterized = bucket.query(airlineQueryParameterized);
for (N1qlQueryRow row : queryResultParameterized) {
System.out.println(row);
}
(I posted a full gist of this example for the imports, etc.)
See the docs for more info, but you may want to use the DSL to allow IDE code completion and Java compile time checking. When developing an interactive web application, you'll probably also want to use parameterized statements (for security) and may even want prepared statements (for performance).
I know I can get the AST using the explain extended command. My question is, how to get the same using the Java API.
My goal is to get the following data about queries:
Database source and target (if applied).
Table source and target (if applied).
Fields involved in the query.
I know I can get them above data directly from query string using Regex, but I want to use Java API.
Do you have any other idea how to do that?
You can use Hive Parser for this. It simply takes the query and convert it into AST which is similar explain command. Here is a simple example:
ParseDriver pd = new ParseDriver();
ASTNode tree = pd.parse("Select * from table1");
System.out.println(tree.dump());
The output for this will be
nil
TOK_QUERY
TOK_FROM
TOK_TABREF
TOK_TABNAME
table1
TOK_INSERT
TOK_DESTINATION
TOK_DIR
TOK_TMP_FILE
TOK_SELECT
TOK_SELEXPR
TOK_ALLCOLREF
<EOF>
Suppose I have some jena query object :
String query = "SELECT * WHERE{ ?s <some_uri> ?o ...etc. }";
Query q = QueryFactory.create(query, Syntax.syntaxARQ);
How would one go about getting information about the jena query object and adding in triples to it iteratively in an effective manner? For example, suppose I wanted to add in the triples
?o dcterms:title "TheBestTitle".
?o dcterms:date ?date.
to the query, and perhaps more.
Is there some way to add in these triples to the query, or do some magic to create a new query object which looks like the original with those triples added in? Assume that I may need to grab information from the original version of the query as well (for example, List resultVars = q.getResultVars();).
Some leads I have are to use the AlgebraGenerator and Op Classes provided by the Jena API, but I can't seem to find any reasonable use cases in a context such as this.
Thanks!
http://jena.apache.org/documentation/query/manipulating_sparql_using_arq.html
Construct an algebra expression and convert to a query (OpAsQuery)
The Query object, which is the cleaned up parsed struture, can be manipulated (Query.getQueryPattern)
Do it by string manipulation before parsing.
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.