diff --git a/grammar/query.pp b/grammar/query.pp
index 7bf7341d2a..098ae65816 100644
--- a/grammar/query.pp
+++ b/grammar/query.pp
@@ -73,11 +73,11 @@ key_value_pair:
   | ::flag_prefix::  flag()  ::colon:: ::space::? boolean() #flag_statement
   | ::field_prefix:: field() ::colon:: ::space::? term()    #field_statement
   |                  field() ::colon:: ::space::? term()    #field_statement
-  | key()   ::space::?       ::lt::    ::space::? value()   #less_than
-  | key()   ::space::?       ::gt::    ::space::? value()   #greater_than
-  | key()   ::space::?       ::lte::   ::space::? value()   #less_than_or_equal_to
-  | key()   ::space::?       ::gte::   ::space::? value()   #greater_than_or_equal_to
-  | field() ::space::?       ::equal:: ::space::? value()   #equal_to
+  | key() ::space::?         ::lt::    ::space::? value()   #less_than
+  | key() ::space::?         ::gt::    ::space::? value()   #greater_than
+  | key() ::space::?         ::lte::   ::space::? value()   #less_than_or_equal_to
+  | key() ::space::?         ::gte::   ::space::? value()   #greater_than_or_equal_to
+  | key() ::space::?         ::equal:: ::space::? value()   #equal_to
 
 #native_key:
     <database>
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FieldEqualsExpression.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FieldEqualsExpression.php
index 8a4b93ca0c..e514fcf312 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FieldEqualsExpression.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/FieldEqualsExpression.php
@@ -2,38 +2,41 @@
 
 namespace Alchemy\Phrasea\SearchEngine\Elastic\AST;
 
+use Alchemy\Phrasea\SearchEngine\Elastic\AST\KeyValue\FieldKey;
+use Alchemy\Phrasea\SearchEngine\Elastic\AST\KeyValue\Key;
 use Alchemy\Phrasea\SearchEngine\Elastic\Exception\QueryException;
 use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryContext;
 use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryHelper;
+use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryPostProcessor;
 
 class FieldEqualsExpression extends Node
 {
-    private $field;
+    private $key;
     private $value;
 
-    public function __construct(Field $field, $value)
+    public function __construct(Key $key, $value)
     {
-        $this->field = $field;
+        $this->key = $key;
         $this->value = $value;
     }
 
     public function buildQuery(QueryContext $context)
     {
-        $structure_field = $context->get($this->field);
-        if (!$structure_field) {
-            throw new QueryException(sprintf('Field "%s" does not exist', $this->field->getValue()));
-        }
-        if (!$structure_field->isValueCompatible($this->value)) {
+        if (!$this->key->isValueCompatible($this->value, $context)) {
             return null;
         }
 
         $query = [
             'term' => [
-                $structure_field->getIndexField(true) => $this->value
+                $this->key->getIndexField($context, true) => $this->value
             ]
         ];
 
-        return QueryHelper::wrapPrivateFieldQuery($structure_field, $query);
+        if ($this->key instanceof QueryPostProcessor) {
+            return $this->key->postProcessQuery($query, $context);
+        }
+
+        return $query;
     }
 
     public function getTermNodes()
@@ -43,6 +46,6 @@ class FieldEqualsExpression extends Node
 
     public function __toString()
     {
-        return sprintf('(%s == <value:"%s">)', $this->field, $this->value);
+        return sprintf('(<%s> == <value:"%s">)', $this->key, $this->value);
     }
 }
diff --git a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/KeyValue/FieldKey.php b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/KeyValue/FieldKey.php
index 84ebed4bbf..e238b41cb1 100644
--- a/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/KeyValue/FieldKey.php
+++ b/lib/Alchemy/Phrasea/SearchEngine/Elastic/AST/KeyValue/FieldKey.php
@@ -19,9 +19,9 @@ class FieldKey implements Key, QueryPostProcessor
         $this->name = $name;
     }
 
-    public function getIndexField(QueryContext $context, ...$other)
+    public function getIndexField(QueryContext $context, $raw = false)
     {
-        return $this->getField($context)->getIndexField(...$other);
+        return $this->getField($context)->getIndexField($raw);
     }
 
     public function isValueCompatible($value, QueryContext $context)
@@ -41,7 +41,8 @@ class FieldKey implements Key, QueryPostProcessor
         if (!isset($this->field_cache[$hash])) {
             $this->field_cache[$hash] = $context->get($this->name);
         }
-        if ($field = $this->field_cache[$hash] === null) {
+        $field = $this->field_cache[$hash];
+        if ($field === null) {
             throw new QueryException(sprintf('Field "%s" does not exist', $this->name));
         }
         return $field;
diff --git a/tests/Alchemy/Tests/Phrasea/SearchEngine/AST/FieldEqualsExpressionTest.php b/tests/Alchemy/Tests/Phrasea/SearchEngine/AST/FieldEqualsExpressionTest.php
index 99dbd0fb6c..d686efffe3 100644
--- a/tests/Alchemy/Tests/Phrasea/SearchEngine/AST/FieldEqualsExpressionTest.php
+++ b/tests/Alchemy/Tests/Phrasea/SearchEngine/AST/FieldEqualsExpressionTest.php
@@ -2,8 +2,8 @@
 
 namespace Alchemy\Tests\Phrasea\SearchEngine\AST;
 
-use Alchemy\Phrasea\SearchEngine\Elastic\AST\Field as ASTField;
 use Alchemy\Phrasea\SearchEngine\Elastic\AST\FieldEqualsExpression;
+use Alchemy\Phrasea\SearchEngine\Elastic\AST\KeyValue\Key;
 use Alchemy\Phrasea\SearchEngine\Elastic\Search\QueryContext;
 use Alchemy\Phrasea\SearchEngine\Elastic\Structure\Field as StructureField;
 
@@ -17,10 +17,10 @@ class FieldEqualsExpressionTest extends \PHPUnit_Framework_TestCase
     public function testSerialization()
     {
         $this->assertTrue(method_exists(FieldEqualsExpression::class, '__toString'), 'Class does not have method __toString');
-        $field = $this->prophesize(ASTField::class);
-        $field->__toString()->willReturn('foo');
-        $node = new FieldEqualsExpression($field->reveal(), 'bar');
-        $this->assertEquals('(foo == <value:"bar">)', (string) $node);
+        $key = $this->prophesize(Key::class);
+        $key->__toString()->willReturn('foo');
+        $node = new FieldEqualsExpression($key->reveal(), 'bar');
+        $this->assertEquals('(<foo> == <value:"bar">)', (string) $node);
     }
 
     /**
@@ -28,20 +28,15 @@ class FieldEqualsExpressionTest extends \PHPUnit_Framework_TestCase
      */
     public function testQueryBuild($index_field, $value, $compatible_value, $private, $expected_json)
     {
-        $structure_field = $this->prophesize(StructureField::class);
-        $structure_field->isValueCompatible($value)->willReturn($compatible_value);
-        $structure_field->getIndexField(true)->willReturn($index_field);
-        $structure_field->isPrivate()->willReturn($private);
-        if ($private) {
-            $structure_field->getDependantCollections()->willReturn(['baz', 'qux']);
-        }
+        $query_context = $this->prophesize(QueryContext::class)->reveal();
 
-        $ast_field = $this->prophesize(ASTField::class);
-        $query_context = $this->prophesize(QueryContext::class);
-        $query_context->get($ast_field->reveal())->willReturn($structure_field);
+        $key = $this->prophesize(Key::class);
+        $key->isValueCompatible($value, $query_context)->willReturn($compatible_value);
+        $key->getIndexField($query_context, true)->willReturn($index_field);
+        // TODO Test keys implementing QueryPostProcessor
 
-        $node = new FieldEqualsExpression($ast_field->reveal(), 'bar');
-        $query = $node->buildQuery($query_context->reveal());
+        $node = new FieldEqualsExpression($key->reveal(), 'bar');
+        $query = $node->buildQuery($query_context);
 
         $this->assertEquals(json_decode($expected_json, true), $query);
     }
@@ -49,14 +44,15 @@ class FieldEqualsExpressionTest extends \PHPUnit_Framework_TestCase
     public function queryProvider()
     {
         return [
-            ['foo.raw', 'bar', true, true, '{
-                "filtered": {
-                    "filter": {
-                        "terms": {
-                            "base_id": ["baz","qux"] } },
-                    "query": {
-                        "term": {
-                            "foo.raw": "bar" } } } }'],
+            // TODO Put this case in another test case
+            // ['foo.raw', 'bar', true, true, '{
+            //     "filtered": {
+            //         "filter": {
+            //             "terms": {
+            //                 "base_id": ["baz","qux"] } },
+            //         "query": {
+            //             "term": {
+            //                 "foo.raw": "bar" } } } }'],
             ['foo.raw', 'bar', true, false, '{
                 "term": {
                     "foo.raw": "bar" } }'],
diff --git a/tests/Alchemy/Tests/Phrasea/SearchEngine/resources/queries.csv b/tests/Alchemy/Tests/Phrasea/SearchEngine/resources/queries.csv
index fa1b37a72b..53e39de0d9 100644
--- a/tests/Alchemy/Tests/Phrasea/SearchEngine/resources/queries.csv
+++ b/tests/Alchemy/Tests/Phrasea/SearchEngine/resources/queries.csv
@@ -61,9 +61,9 @@ foo < "2015/01/01"|<range:field.foo lt="2015/01/01">
 foo ≤ "2015/01/01"|<range:field.foo lte="2015/01/01">
 foo > "2015/01/01"|<range:field.foo gt="2015/01/01">
 foo ≥ "2015/01/01"|<range:field.foo gte="2015/01/01">
-foo = 42|(<field:foo> == <value:"42">)
-foo = bar|(<field:foo> == <value:"bar">)
-foo = "bar"|(<field:foo> == <value:"bar">)
+foo = 42|(<field.foo> == <value:"42">)
+foo = bar|(<field.foo> == <value:"bar">)
+foo = "bar"|(<field.foo> == <value:"bar">)
 
 # Field narrowing
 foo:bar|(<field:foo> MATCHES <text:"bar">)
@@ -109,6 +109,7 @@ meta.Duration < 300|<range:metadata.Duration lt="300">
 meta.Duration ≤ 300|<range:metadata.Duration lte="300">
 meta.Duration > 300|<range:metadata.Duration gt="300">
 meta.Duration ≥ 300|<range:metadata.Duration gte="300">
+meta.Duration = 300|(<metadata.Duration> == <value:"300">)
 
 # Unescaped "." issue on key prefixes
 fieldOne:foo|(<field:fieldOne> MATCHES <text:"foo">)