[#7116] Add Field.collate(Collation) and collate(String) to support COLLATE clauses

jOOQ/src/main/java/org/jooq/Field.java

@@ -108,6 +108,7 @@ public interface Field<T> extends SelectField<T>, GroupField, OrderField<T>, Fie
      * expressions return the empty string <code>""</code> here, never
      * <code>null</code>.
      */
+    @Override
     String getComment();
 
     /**
@@ -3324,6 +3325,28 @@ public interface Field<T> extends SelectField<T>, GroupField, OrderField<T>, Fie
     @Support({ CUBRID, FIREBIRD, H2, HSQLDB, MARIADB, MYSQL, POSTGRES })
     Field<Integer> ascii();
 
+    /**
+     * Apply a collation operator to this column expression.
+     *
+     * @see DSL#collation(String)
+     */
+    @Support({ HSQLDB, MARIADB, MYSQL, POSTGRES, SQLITE })
+    Field<String> collate(String collation);
+
+    /**
+     * Apply a collation operator to this column expression.
+     *
+     * @see DSL#collation(Name)
+     */
+    @Support({ HSQLDB, MARIADB, MYSQL, POSTGRES, SQLITE })
+    Field<String> collate(Name collation);
+
+    /**
+     * Apply a collation operator to this column expression.
+     */
+    @Support({ HSQLDB, MARIADB, MYSQL, POSTGRES, SQLITE })
+    Field<String> collate(Collation collation);
+
     /**
      * This method is part of the pre-2.0 API. This API is maintained for
      * backwards-compatibility. It may be removed in the future. Consider using

jOOQ/src/main/java/org/jooq/impl/AbstractField.java

@@ -80,6 +80,7 @@ import org.jooq.Binding;
 import org.jooq.CaseValueStep;
 import org.jooq.CaseWhenStep;
 import org.jooq.Clause;
+import org.jooq.Collation;
 import org.jooq.Comment;
 import org.jooq.Comparator;
 import org.jooq.Condition;
@@ -1901,6 +1902,21 @@ abstract class AbstractField<T> extends AbstractNamed implements Field<T> {
         return DSL.ascii(varchar());
     }
 
+    @Override
+    public final Field<String> collate(String collation) {
+        return collate(DSL.collation(collation));
+    }
+
+    @Override
+    public final Field<String> collate(Name collation) {
+        return collate(DSL.collation(collation));
+    }
+
+    @Override
+    public final Field<String> collate(Collation collation) {
+        return new CollatedField(this, collation);
+    }
+
     @Override
     @Deprecated
     public final Field<String> concat(Field<?>... fields) {

jOOQ/src/main/java/org/jooq/impl/CollatedField.java

@@ -0,0 +1,79 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Other licenses:
+ * -----------------------------------------------------------------------------
+ * Commercial licenses for this work are available. These replace the above
+ * ASL 2.0 and offer limited warranties, support, maintenance, and commercial
+ * database integrations.
+ *
+ * For more information, please visit: http://www.jooq.org/licenses
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ *
+ */
+package org.jooq.impl;
+
+import static org.jooq.impl.Keywords.K_COLLATE;
+
+import org.jooq.Binding;
+import org.jooq.Collation;
+import org.jooq.Context;
+import org.jooq.DataType;
+import org.jooq.Field;
+
+/**
+ * @author Lukas Eder
+ */
+final class CollatedField extends AbstractField<String> {
+
+    private static final long serialVersionUID = -3996395622492844215L;
+    private final Field<?>    field;
+    private final Collation   collation;
+
+    CollatedField(Field<?> field, Collation collation) {
+        super(field.getQualifiedName(), type(field), DSL.comment(field.getComment()), binding(field));
+
+        this.field = field;
+        this.collation = collation;
+    }
+
+    @SuppressWarnings("unchecked")
+    private static final Binding<?, String> binding(Field<?> field) {
+        return field.getType() == String.class ? (Binding<?, String>) field.getBinding() : SQLDataType.VARCHAR.getBinding();
+    }
+
+    @SuppressWarnings("unchecked")
+    private static final DataType<String> type(Field<?> field) {
+        return field.getType() == String.class ? (DataType<String>) field.getDataType() : SQLDataType.VARCHAR;
+    }
+
+    @Override
+    public final void accept(Context<?> ctx) {
+        ctx.sql("((").visit(field).sql(") ").visit(K_COLLATE).sql(' ').visit(collation).sql(')');
+
+    }
+}

jOOQ/src/main/java/org/jooq/impl/Keywords.java

@@ -77,6 +77,8 @@ final class Keywords {
     static final Keyword K_CHANGE_COLUMN                    = keyword("change column");
     static final Keyword K_CHECK                            = keyword("check");
     static final Keyword K_COALESCE                         = keyword("coalesce");
+    static final Keyword K_COLLATE                          = keyword("collate");
+    static final Keyword K_COLLATION                        = keyword("collation");
     static final Keyword K_COLUMN                           = keyword("column");
     static final Keyword K_COLUMNS                          = keyword("columns");
     static final Keyword K_COMMENT                          = keyword("comment");