Criteria. Make Path a concrete class and enrich with fluent methods

criteria/common/src/org/immutables/criteria/constraints/CriteriaContext.java

@@ -38,7 +38,7 @@ public R create() {
    *  adds an intermediate step (list of paths usually)
    */
   public CriteriaContext<R> add(Path path) {
-    final Path newPath = this.path != null ? Expressions.path(this.path.path() + "." + path.path()) : path;
+    final Path newPath = this.path != null ? this.path.concat(path) : path;
     return new CriteriaContext<>(operator, expression, newPath, creator);
   }
 

criteria/common/src/org/immutables/criteria/constraints/DebugExpressionVisitor.java

@@ -40,7 +40,7 @@ public Void visit(Literal literal) {
   @Override
   public Void visit(Path path) {
     writer.print(" path=");
-    writer.print(path.path());
+    writer.print(path.toStringPath());
     return null;
   }
 }

criteria/common/src/org/immutables/criteria/constraints/Expressions.java

@@ -19,20 +19,7 @@ public final class Expressions {
   private Expressions() {}
 
   public static Path path(final String path) {
-    Preconditions.checkNotNull(path, "path");
-
-    return new Path() {
-      @Override
-      public String path() {
-        return path;
-      }
-
-      @Nullable
-      @Override
-      public <R, C> R accept(ExpressionBiVisitor<R, C> visitor, @Nullable C context) {
-        return visitor.visit(this, context);
-      }
-    };
+    return Path.of(path);
   }
 
   public static Literal nullLiteral(Class<?> type) {

criteria/common/src/org/immutables/criteria/constraints/Path.java

@@ -1,10 +1,59 @@
 package org.immutables.criteria.constraints;
 
+import com.google.common.base.Preconditions;
+import com.google.common.collect.ImmutableList;
+
+import javax.annotation.Nullable;
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
 /**
- * Access to a field.
+ * Access to a property possibly via several paths like {@code foo.bar.qux}
  */
-public interface Path extends Expression {
+public final class Path implements Expression {
+
+  private final ImmutableList<String> paths;
+
+  private Path(List<String> paths) {
+    this.paths = ImmutableList.copyOf(paths);
+  }
+
+  public List<String> paths() {
+    return paths;
+  }
+
+  public Path add(String path) {
+    Objects.requireNonNull(path, "path");
+    Preconditions.checkArgument(!path.isEmpty(), "empty path");
+    return new Path(ImmutableList.<String>builder().addAll(paths).add(path).build());
+  }
+
+  public Path concat(Path other) {
+    Objects.requireNonNull(other, "other");
+    return new Path(ImmutableList.<String>builder().addAll(this.paths).addAll(other.paths).build());
+  }
+
+  public static Path of(String path) {
+    Objects.requireNonNull(path);
+    return new Path(Collections.singletonList(path));
+  }
+
+  /**
+   * Returns current path in java bean format: {@code foo.bar.qux}
+   */
+  public String toStringPath() {
+    return String.join(".", paths());
+  }
 
-  String path();
+  @Override
+  public String toString() {
+    return toStringPath();
+  }
 
+  @Nullable
+  @Override
+  public <R, C> R accept(ExpressionBiVisitor<R, C> visitor, @Nullable C context) {
+    return visitor.visit(this, context);
+  }
 }

criteria/elasticsearch/src/org/immutables/criteria/elasticsearch/ElasticsearchQueryVisitor.java

@@ -77,7 +77,7 @@ public String visit(Literal literal) {
 
     @Override
     public String visit(Path path) {
-      return path.path();
+      return path.toStringPath();
     }
   }
 }

criteria/inmemory/src/org.immutables.criteria.inmemory/InMemoryExpressionEvaluator.java

@@ -193,13 +193,13 @@ public Object visit(Literal literal) {
 
     @Override
     public Object visit(Path path) {
-      return extractor.extract(path.path());
+      return extractor.extract(path);
     }
   }
 
   private interface ValueExtractor<T> {
     @Nullable
-    Object extract(String property);
+    Object extract(Path path);
   }
 
   private static class ReflectionFieldExtractor<T> implements ValueExtractor<T> {
@@ -211,20 +211,19 @@ private ReflectionFieldExtractor(T object) {
 
     @Nullable
     @Override
-    public Object extract(String property) {
-      Objects.requireNonNull(property, "property");
+    public Object extract(Path path) {
+      Objects.requireNonNull(path, "path");
 
       Object result = object;
 
-      for (String name:property.split("\\.")) {
+      for (String name:path.paths()) {
         result = extract(result, name);
         if (result == UNKNOWN) {
           break;
         }
       }
 
       return result;
-
     }
 
     private static Object extract(Object instance, String property) {
@@ -247,6 +246,7 @@ private static Object extract(Object instance, String property) {
         throw new RuntimeException(e);
       }
     }
+
   }
 
 }

criteria/mongo/src/org/immutables/criteria/mongo/MongoVisitor.java

@@ -96,6 +96,6 @@ public BsonValue visit(Literal literal) {
 
   @Override
   public BsonString visit(Path path) {
-    return new BsonString(path.path());
+    return new BsonString(path.toStringPath());
   }
 }