Using the Elasticsearch High Level REST Client for Java v7.3
I have a few fields in the schema that look like this:
{
"document_type" : ["Utility", "Credit"]
}
Basically one field could have an array of strings as the value. I not only need to query for a specific document_type, but also a general string query.
I've tried the following code:
QueryBuilder query = QueryBuilders.boolQuery()
.must(QueryBuilders.queryStringQuery(terms))
.filter(QueryBuilders.termQuery("document_type", "Utility"));
...which does not return any results. If I remove the ".filter()" part the query returns fine, but the filter appears to prevent any results from coming back. I'm suspecting it's because document_type is a multi-valued array - maybe I'm wrong though. How would I build a query query all documents for specific terms, but also filter by document_type?
I think, the reason is the wrong query. Consider using the terms query instead of term query. There is also a eqivalent in the java api.
Here is a good overview of the query qsl queries and their eqivalent in the high level rest client: https://www.elastic.co/guide/en/elasticsearch/client/java-rest/current/java-rest-high-query-builders.html
I'm currecntly trying to test out some new score functions on my Elasticsearch query but I'm not yielding the results I am expecting.
I found this on their site about explaining queries here
I can run as a curl command but does anyone know how to translate this to use the Java api?
If you're using the ES5 Java API, you can get the explanation like this:
QueryBuilder query = matchAllQuery(); // your query
ExplainRequest request = new ExplainRequest("index", "type", "id").query(query);
ExplainResponse explainResponse = client.explain(request).actionGet();
Explanation explanation = explainResponse.getExplanation();
Where client is your org.elasticsearch.client.Client instance.
I am quite new to Java Sesame and SPARQL. I have added statements into the Sesame repository and am now trying to retrieve some statements and simply print them. From what I understood that I need to parse the query in order to print the retrieved statements. The code below shows where I have reached so far:
String queryString = "SELECT ?subject ?object WHERE { ?subject <http://example.org/is> ?object . } LIMIT 1";
...
SPARQLParser parser = new SPARQLParser();
ParsedQuery query = parser.parseQuery(queryString, null);
StatementPatternCollector collector = new StatementPatternCollector();
query.getTupleExpr().visit(collector);
List<StatementPattern> patterns = collector.getStatementPatterns();
// To print the first statement only for example.
System.out.println(patterns.get(0));
Here is the output:
StatementPattern
Var (name=name)
Var (name=-const-1, value=http://example.org/is, anonymous)
Var (name=object)
According to the output, it does not show me the subject and object. My questions are: How can I print the results of the query as shown above. Is this code the right way to parse the query for printing the statements later. Your help would be very much appreciated.
You get the results of a query by evaluating the query, not by parsing it. What your code does is inspect the query's algebra model and retrieve patterns from that algebra. This approach will not give you query results.
Evaluating a query in Sesame is far simpler than this:
// open a connection to the Sesame repository containing your statements
RepositoryConnection conn = repository.getConnection();
try {
// create a prepared query object from your query string
TupleQuery query = conn.prepareTupleQuery(QueryLanguage.SPARQL, queryString);
// evaluate the query on the repository
TupleQueryResult result = query.evaluate();
// iterate over the results and do something with each result
while (result.hasNext()) {
BindingSet s = result.next();
Value subject = s.getValue("subject");
Value object = s.getValue("object");
System.out.println("value of ?subject: " + subject);
System.out.println("value of ?object: " + object);
}
} finally {
conn.close();
}
As Joshua pointed out, your query retrieves variable bindings (for the variables mentioned in your SELECT clause), not RDF statements. You can of course re-create the RDF statement from those variable bindings in Java, but if you really want full statements rather than just the subject and object, it's probably easier to switch to using a SPARQL CONSTRUCT query instead of a SELECT query.
For more information on how to evaluate different kinds of queries and work with the results in Sesame, see the Sesame user documentation (section 6.5 in particular) and the API Javadoc.
I'm trying to build a small semantic web application using Jena framework, JSP and JAVA. I have a remote SPARQL endpoint and I've already written a simple query which works fine but now I need to use some parameters. Here is my code so far:
final static String serviceEndpoint = "http://fishdelish.cs.man.ac.uk/sparql/";
String comNameQuery =
"PREFIX fd: <http://fishdelish.cs.man.ac.uk/rdf/vocab/resource/> " +
"SELECT ?name ?language ?type" +
"WHERE { ?nameID fd:comnames_ComName ?name ;" +
"fd:comnames_Language ?language ;" +
"fd:comnames_NameType ?type ." +
"}";
Query query = QueryFactory.create(comNameQuery);
QueryExecution qe = QueryExecutionFactory.sparqlService(serviceEndpoint,query);
try {
ResultSet rs = qe.execSelect();
if ( rs.hasNext() ) {
System.out.println(ResultSetFormatter.asText(rs));
}
}
catch(Exception e) {
System.out.println(e.getMessage());
}
finally {
qe.close();
}
What I want to do is to parameterized ?name. I'm new to Jena and I'm not really sure how to use parameters in a SPARQL query. I would appreciate it if someone could help me with this.
If you just want to restrict a variable to have a certain value for local queries you can do so with an overload of the QueryFactory.create() method which takes a QuerySolutionMap to set value restrictions. Note this doesn't alter your query just restricts the final results so this is not really parameterization.
If you want to actually have true parameterized queries (i.e. substitute variables for constants) then there are a couple of ways to do this depending on your version of ARQ.
Using any current release (up to 2.9.0) the only way to do it is string concatenation i.e. instead of having ?name in your query you would just insert the value you want e.g. "Bob"
Using the latest trunk (2.9.1-SNAPSHOT onwards) there is a new ParameterizedSparqlString class which makes this much more user friendly e.g.
ParameterizedSparqlString queryStr = new ParameterizedSparqlString(comNameQuery);
queryStr.setLiteral("name", "Bob");
Query query = QueryFactory.create(queryStr.toString());
And in fact you can simplify your code further since ParameterizedSparqlString has a StringBuffer style interface and can be used to build your query bit by bit and includes useful functionality like prepending prefixes to your query.
The advantage of this new method is that it provides a more generic way of doing parameterized queries that can also be used with updates and is usable for preparing remote queries which the existing methods do not cover.
You could try looking into Twinkql. It is a SPARQL-to-Java mapping framework. It uses Jena in the back end, but tries to simplify SPARQL queries and Java binding of the results.
It allows you to define SPARQL queries in xml:
<select id="getNovel" resultMap="novelResultMap">
<![CDATA[
SELECT ?novel ?author
WHERE {
?novel a <http://dbpedia.org/class/yago/EnglishNovels> ;
<http://dbpedia.org/property/name> "#{novelName}"#en ;
<http://dbpedia.org/property/author> ?author .
}
]]>
</select>
Note the #{novelName} placeholder -- this is where parameters can be passed in at query time.
Also, results can be bound to Java Beans:
<resultMap id="novelResultMap" resultClass="org.twinkql.example.Novel">
<uniqueResult>novel</uniqueResult>
<rowMap var="novel" varType="localName" beanProperty="name" />
<rowMap var="author" varType="localName" beanProperty="author"/>
</resultMap>
There is an API to call these queries, to pass in parameters, etc. It is much like MyBatis, but for SPARQL instead of SQL.
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.