Examples of org.apache.metamodel.DataContext.query()

org.apache.metamodel.DataContext.query()
Starts building a query using the query builder API. This way of building queries is the preferred approach since it provides a more type-safe approach to building API's as well as allows the DataContext implementation to be aware of the query building process. @return a query builder component at the initial position in building aquery.

    DataContext converted = Converters.addTypeConverter(source, fooColumn,
        new StringToIntegerConverter());


    // only select "bar" which is not converted
    Table table = converted.getDefaultSchema().getTableByName("table");
    Query query = converted.query().from(table).select("bar").toQuery();
    assertEquals("SELECT table.bar FROM schema.table", query.toSql());


    DataSet ds = converted.executeQuery(query);
    assertEquals(InMemoryDataSet.class, ds.getClass());

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    public void testInconsistentColumns() throws Exception {
        CsvConfiguration conf = new CsvConfiguration(CsvConfiguration.DEFAULT_COLUMN_NAME_LINE, "UTF8", ',', '"', '\\',
                true);
        DataContext dc = new CsvDataContext(new File("src/test/resources/csv_inconsistent_columns.csv"), conf);
        DataSet ds = dc.query().from("csv_inconsistent_columns.csv").select("hello").and("world").execute();
        assertTrue(ds.next());
        assertTrue(ds.next());


        try {
            ds.next();

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    public void testApproximatedCountSmallFile() throws Exception {
        DataContext dc = new CsvDataContext(new File("src/test/resources/csv_people.csv"));


        Table table = dc.getDefaultSchema().getTables()[0];
        Query q = dc.query().from(table).selectCount().toQuery();
        SelectItem selectItem = q.getSelectClause().getItem(0);
        selectItem.setFunctionApproximationAllowed(true);


        DataSet ds = dc.executeQuery(q);
        assertTrue(ds.next());

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    public void testOffsetAndMaxrows() throws Exception {
        DataContext dc = new CsvDataContext(new File("src/test/resources/csv_people.csv"));


        Table table = dc.getDefaultSchema().getTables()[0];
        Query q = dc.query().from(table).select(table.getColumnByName("name")).toQuery();
        q.setFirstRow(3);
        q.setMaxRows(2);


        DataSet ds;

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        dc = Converters.addTypeConverters(dc, converters);


        Table table = dc.getDefaultSchema().getTables()[0];
        MutableColumn col = (MutableColumn) table.getColumns()[0];
        Query q = dc.query().from(table).select(col).toQuery();
        assertEquals("SELECT csv_only_number_one.csv.number FROM resources.csv_only_number_one.csv", q.toSql());


        DataSet ds = dc.executeQuery(q);
        while (ds.next()) {
            assertEquals(true, ds.getRow().getValue(0));

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        assertEquals(1, table.getColumnByName("i").getColumnSize().intValue());
        assertEquals(8, table.getColumnByName("greeting").getColumnSize().intValue());
        assertEquals(7, table.getColumnByName("greeter").getColumnSize().intValue());


        Query q = dc.query().from(table).select(table.getColumns()).toQuery();
        DataSet ds = dc.executeQuery(q);


        assertTrue(ds.next());
        assertEquals("[1, hello, world]", Arrays.toString(ds.getRow().getValues()));
        assertTrue(ds.next());

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                        7 }, false));


        Table table = dc.getDefaultSchema().getTables()[0];
        assertEquals("[i, greet, inggree]", Arrays.toString(table.getColumnNames()));


        Query q = dc.query().from(table).select(table.getColumns()).toQuery();
        DataSet ds = dc.executeQuery(q);


        assertTrue(ds.next());
        assertEquals("[1, hello, worl]", Arrays.toString(ds.getRow().getValues()));
        assertTrue(ds.next());

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                        9 }, false));


        Table table = dc.getDefaultSchema().getTables()[0];
        assertEquals("[i, greeting, greeter]", Arrays.toString(table.getColumnNames()));


        Query q = dc.query().from(table).select(table.getColumns()).toQuery();
        DataSet ds = dc.executeQuery(q);


        assertTrue(ds.next());
        assertEquals("[1, hello, world]", Arrays.toString(ds.getRow().getValues()));
        assertTrue(ds.next());

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    Column colA = new MutableColumn("colA", null, tableAB, 0, true);
    Column colB = new MutableColumn("colB", null, tableAB, 1, true);
    Column colC = new MutableColumn("colC", null, tableC, 0, true);


    Query q = dc.query().from(tableAB).leftJoin(tableC).on(colB, colC)
        .select(colA).as("a").select(colB).as("b").select(colC).as("c")
        .toQuery();


    assertEquals(
        "SELECT tableAB.colA AS a, tableAB.colB AS b, tableC.colC AS c FROM tableAB LEFT JOIN tableC ON tableAB.colB = tableC.colC",

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          public DataSet intercept(DataSet dataSet) {
            return new MaxRowsDataSet(dataSet, 1);
          }
        });


    DataSet ds = dc.query().from(table).select("foo").execute();
    assertEquals(MaxRowsDataSet.class, ds.getClass());
    assertEquals(1, ds.toObjectArrays().size());
  }


  public void testInterceptQuery() throws Exception {

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