2222import com .mongodb .DBObject ;
2323
2424/**
25- * Encapsulates the aggregation framework {@code $lookup}-operation.
26- * We recommend to use the static factory method {@link Aggregation#lookup(String, String, String, String)} instead of
27- * creating instances of this class directly.
25+ * Encapsulates the aggregation framework {@code $lookup}-operation. We recommend to use the static factory method
26+ * {@link Aggregation#lookup(String, String, String, String)} instead of creating instances of this class directly.
2827 *
2928 * @author Alessio Fachechi
29+ * @author Christoph Strobl
3030 * @see http://docs.mongodb.org/manual/reference/aggregation/lookup/#stage._S_lookup
3131 * @since 1.9
3232 */
33- public class LookupOperation implements AdditionalFieldsExposingAggregationOperation {
33+ public class LookupOperation implements FieldsExposingAggregationOperation {
3434
35- private ExposedField from ;
36- private ExposedField localField ;
37- private ExposedField foreignField ;
35+ private Field from ;
36+ private Field localField ;
37+ private Field foreignField ;
3838 private ExposedField as ;
3939
4040 /**
@@ -46,24 +46,38 @@ public class LookupOperation implements AdditionalFieldsExposingAggregationOpera
4646 * @param as must not be {@literal null}.
4747 */
4848 public LookupOperation (Field from , Field localField , Field foreignField , Field as ) {
49+
4950 Assert .notNull (from , "From must not be null!" );
5051 Assert .notNull (localField , "LocalField must not be null!" );
5152 Assert .notNull (foreignField , "ForeignField must not be null!" );
5253 Assert .notNull (as , "As must not be null!" );
5354
54- this .from = new ExposedField ( from , true ) ;
55- this .localField = new ExposedField ( localField , true ) ;
56- this .foreignField = new ExposedField ( foreignField , true ) ;
55+ this .from = from ;
56+ this .localField = localField ;
57+ this .foreignField = foreignField ;
5758 this .as = new ExposedField (as , true );
5859 }
5960
61+ private LookupOperation () {
62+ // used by builder
63+ }
64+
65+ /*
66+ * (non-Javadoc)
67+ * @see org.springframework.data.mongodb.core.aggregation.FieldsExposingAggregationOperation#getFields()
68+ */
6069 @ Override
6170 public ExposedFields getFields () {
6271 return ExposedFields .from (as );
6372 }
6473
74+ /*
75+ * (non-Javadoc)
76+ * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#toDBObject(org.springframework.data.mongodb.core.aggregation.AggregationOperationContext)
77+ */
6578 @ Override
6679 public DBObject toDBObject (AggregationOperationContext context ) {
80+
6781 BasicDBObject lookupObject = new BasicDBObject ();
6882
6983 lookupObject .append ("from" , from .getTarget ());
@@ -73,4 +87,106 @@ public DBObject toDBObject(AggregationOperationContext context) {
7387
7488 return new BasicDBObject ("$lookup" , lookupObject );
7589 }
90+
91+ /**
92+ * Get a builder that allows creation of {@link LookupOperation}.
93+ *
94+ * @return
95+ */
96+ public static FromBuilder newLookup () {
97+ return new LookupOperationBuilder ();
98+ }
99+
100+ public static interface FromBuilder {
101+
102+ /**
103+ * @param name
104+ * @return
105+ */
106+ LocalFieldBuilder from (String name );
107+ }
108+
109+ public static interface LocalFieldBuilder {
110+
111+ /**
112+ * @param name
113+ * @return
114+ */
115+ ForeignFieldBuilder localField (String name );
116+ }
117+
118+ public static interface ForeignFieldBuilder {
119+
120+ /**
121+ * @param name
122+ * @return
123+ */
124+ AsBuilder foreignField (String name );
125+ }
126+
127+ public static interface AsBuilder {
128+
129+ /**
130+ * @param name
131+ * @return
132+ */
133+ LookupOperation as (String name );
134+ }
135+
136+ /**
137+ * Builder for fluent {@link LookupOperation} creation.
138+ *
139+ * @author Christoph Strobl
140+ * @since 1.9
141+ */
142+ public static final class LookupOperationBuilder
143+ implements FromBuilder , LocalFieldBuilder , ForeignFieldBuilder , AsBuilder {
144+
145+ private LookupOperation lookupOperation ;
146+
147+ private LookupOperationBuilder () {
148+ this .lookupOperation = new LookupOperation ();
149+ }
150+
151+ /**
152+ * Creates new builder for {@link LookupOperation}.
153+ *
154+ * @return never {@literal null}.
155+ */
156+ public static FromBuilder newBuilder () {
157+ return new LookupOperationBuilder ();
158+ }
159+
160+ @ Override
161+ public LocalFieldBuilder from (String name ) {
162+
163+ Assert .hasText (name , "'From' must not be null or empty!" );
164+ lookupOperation .from = Fields .field (name );
165+ return this ;
166+ }
167+
168+ @ Override
169+ public LookupOperation as (String name ) {
170+
171+ Assert .hasText (name , "'As' must not be null or empty!" );
172+ lookupOperation .as = new ExposedField (Fields .field (name ), true );
173+ return null ;
174+ }
175+
176+ @ Override
177+ public AsBuilder foreignField (String name ) {
178+
179+ Assert .hasText (name , "'ForeignField' must not be null or empty!" );
180+ lookupOperation .foreignField = Fields .field (name );
181+ return this ;
182+ }
183+
184+ @ Override
185+ public ForeignFieldBuilder localField (String name ) {
186+
187+ Assert .hasText (name , "'LocalField' must not be null or empty!" );
188+ lookupOperation .localField = Fields .field (name );
189+ return this ;
190+ }
191+ }
76192}
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