DATAJDBC-547 - Polishing.

Let SqlIdentifier implement Streamable<SqlIdentifier> to allow iteration of composed identifiers.
Adapt dialect to iteration changes.

Rewrite simple if blocks to using ternary operators.

Original pull request: #221.

spring-data-relational/src/main/java/org/springframework/data/relational/core/dialect/PostgresDialect.java

@@ -21,6 +21,7 @@ import org.springframework.data.relational.core.sql.IdentifierProcessing;
 import org.springframework.data.relational.core.sql.IdentifierProcessing.LetterCasing;
 import org.springframework.data.relational.core.sql.IdentifierProcessing.Quoting;
 import org.springframework.data.relational.core.sql.LockOptions;
+import org.springframework.data.relational.core.sql.SqlIdentifier;
 import org.springframework.data.relational.core.sql.Table;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -132,9 +133,16 @@ public class PostgresDialect extends AbstractDialect {
 				return "";
 			}
 
-			String tableName = tables.get(0) // get the first table
+			// get the first table and obtain last part if the identifier is a composed one.
-					.getName().getSimpleIdentifier() // without schema
+			SqlIdentifier identifier = tables.get(0).getName();
-					.toSql(this.identifierProcessing);
+			SqlIdentifier last = identifier;
+
+			for (SqlIdentifier sqlIdentifier : identifier) {
+				last = sqlIdentifier;
+			}
+
+			// without schema
+			String tableName = last.toSql(this.identifierProcessing);
 
 			switch (lockOptions.getLockMode()) {
 

spring-data-relational/src/main/java/org/springframework/data/relational/core/mapping/DerivedSqlIdentifier.java

@@ -15,6 +15,8 @@
  */
 package org.springframework.data.relational.core.mapping;
 
+import java.util.Collections;
+import java.util.Iterator;
 import java.util.function.UnaryOperator;
 
 import org.springframework.data.relational.core.sql.IdentifierProcessing;
@@ -40,6 +42,15 @@ class DerivedSqlIdentifier implements SqlIdentifier {
 		this.quoted = quoted;
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.relational.domain.SqlIdentifier#iterator()
+	 */
+	@Override
+	public Iterator<SqlIdentifier> iterator() {
+		return Collections.<SqlIdentifier> singleton(this).iterator();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.relational.domain.SqlIdentifier#transform(java.util.function.UnaryOperator)
@@ -106,11 +117,6 @@ class DerivedSqlIdentifier implements SqlIdentifier {
 	 */
 	@Override
 	public String toString() {
-
+		return quoted ? toSql(IdentifierProcessing.ANSI) : this.name;
-		if (quoted) {
-			return toSql(IdentifierProcessing.ANSI);
-		}
-
-		return this.name;
 	}
 }

spring-data-relational/src/main/java/org/springframework/data/relational/core/mapping/RelationalPersistentEntityImpl.java

@@ -103,6 +103,6 @@ class RelationalPersistentEntityImpl<T> extends BasicPersistentEntity<T, Relatio
 	 */
 	@Override
 	public String toString() {
-		return String.format("JdbcPersistentEntityImpl<%s>", getType());
+		return String.format("RelationalPersistentEntityImpl<%s>", getType());
 	}
 }

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/CompositeSqlIdentifier.java

@@ -15,6 +15,8 @@
  */
 package org.springframework.data.relational.core.sql;
 
+import java.util.Arrays;
+import java.util.Iterator;
 import java.util.StringJoiner;
 import java.util.function.UnaryOperator;
 
@@ -40,6 +42,15 @@ class CompositeSqlIdentifier implements SqlIdentifier {
 		this.parts = parts;
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.relational.domain.SqlIdentifier#iterator()
+	 */
+	@Override
+	public Iterator<SqlIdentifier> iterator() {
+		return Arrays.asList(parts).iterator();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.relational.domain.SqlIdentifier#transform(java.util.function.UnaryOperator)
@@ -71,12 +82,7 @@ class CompositeSqlIdentifier implements SqlIdentifier {
 	 */
 	@Override
 	public String getReference(IdentifierProcessing processing) {
-		throw new UnsupportedOperationException("A Composite SQL Identifiers can't be used as a reference name");
+		throw new UnsupportedOperationException("Composite SQL Identifiers can't be used for reference name retrieval");
-	}
-
-	@Override
-	public SqlIdentifier getSimpleIdentifier() {
-		return parts[parts.length - 1];
 	}
 
 	/*
@@ -86,11 +92,14 @@ class CompositeSqlIdentifier implements SqlIdentifier {
 	@Override
 	public boolean equals(Object o) {
 
-		if (this == o)
+		if (this == o) {
 			return true;
+		}
+
 		if (o instanceof SqlIdentifier) {
 			return toString().equals(o.toString());
 		}
+
 		return false;
 	}
 

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/DefaultSqlIdentifier.java

@@ -15,6 +15,8 @@
  */
 package org.springframework.data.relational.core.sql;
 
+import java.util.Collections;
+import java.util.Iterator;
 import java.util.function.UnaryOperator;
 
 import org.springframework.util.Assert;
@@ -39,6 +41,15 @@ class DefaultSqlIdentifier implements SqlIdentifier {
 		this.quoted = quoted;
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.relational.domain.SqlIdentifier#iterator()
+	 */
+	@Override
+	public Iterator<SqlIdentifier> iterator() {
+		return Collections.<SqlIdentifier> singleton(this).iterator();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.relational.domain.SqlIdentifier#transform(java.util.function.UnaryOperator)
@@ -102,11 +113,6 @@ class DefaultSqlIdentifier implements SqlIdentifier {
 	 */
 	@Override
 	public String toString() {
-
+		return quoted ? toSql(IdentifierProcessing.ANSI) : this.name;
-		if (quoted) {
-			return toSql(IdentifierProcessing.ANSI);
-		}
-
-		return this.name;
 	}
 }

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/SqlIdentifier.java

@@ -15,8 +15,12 @@
  */
 package org.springframework.data.relational.core.sql;
 
+import java.util.Collections;
+import java.util.Iterator;
 import java.util.function.UnaryOperator;
 
+import org.springframework.data.util.Streamable;
+
 /**
  * Represents a named object that exists in the database like a table name or a column name. SQL identifiers are created
  * from a {@link String name} with specifying whether the name should be quoted or unquoted.
@@ -28,18 +32,27 @@ import java.util.function.UnaryOperator;
  * <p>
  * {@link SqlIdentifier} objects are immutable. Calling transformational methods such as
  * {@link #transform(UnaryOperator)} creates a new instance.
+ * <p>
+ * {@link SqlIdentifier} are composable so an identifier may consist of a single identifier part or can be composed from
+ * multiple parts. Composed identifier can be traversed with {@link #stream()} or {@link #iterator()}. The iteration
+ * order depends on the actual composition ordering.
  *
  * @author Jens Schauder
  * @author Mark Paluch
  * @since 2.0
  */
-public interface SqlIdentifier {
+public interface SqlIdentifier extends Streamable<SqlIdentifier> {
 
 	/**
 	 * Null-object.
 	 */
 	SqlIdentifier EMPTY = new SqlIdentifier() {
 
+		@Override
+		public Iterator<SqlIdentifier> iterator() {
+			return Collections.emptyIterator();
+		}
+
 		@Override
 		public SqlIdentifier transform(UnaryOperator<String> transformationFunction) {
 			return this;
@@ -99,16 +112,6 @@ public interface SqlIdentifier {
 	 */
 	SqlIdentifier transform(UnaryOperator<String> transformationFunction);
 
-	/**
-	 * Returns the last part of an identifier. For a fully qualified column name {@literal schema.table.column} it will
-	 * just return the column part. If the identifier consists of only a single part, that part is returned.
-	 *
-	 * @return Guaranteed to be not {@literal null}.
-	 */
-	default SqlIdentifier getSimpleIdentifier() {
-		return this;
-	}
-
 	/**
 	 * Create a new quoted identifier given {@code name}.
 	 *