Fix check constraint support for MariaDB >= 10.2.1 (#1668)

* fixed the check constraint support for mysql/mariadb

* update migration scripts

src/main/java/io/ebeaninternal/dbmigration/ddlgeneration/platform/BaseTableDdl.java

@@ -262,7 +262,6 @@ public class BaseTableDdl implements TableDdl {
     DdlBuffer apply = writer.apply();
     apply.append(platformDdl.getCreateTableCommandPrefix()).append(" ").append(tableName).append(" (");
     writeTableColumns(apply, columns, useIdentity);
-    writeCheckConstraints(apply, createTable);
     writeUniqueConstraints(apply, createTable);
     writeCompoundUniqueConstraints(apply, createTable);
     if (!pk.isEmpty()) {
@@ -506,31 +505,6 @@ public class BaseTableDdl implements TableDdl {
     buffer.appendStatement(platformDdl.dropSequence(sequenceName));
   }
 
-  /**
-   * Write all the check constraints.
-   */
-  protected void writeCheckConstraints(DdlBuffer apply, CreateTable createTable) throws IOException {
-
-    for (Column column : createTable.getColumn()) {
-      String checkConstraint = column.getCheckConstraint();
-      if (hasValue(checkConstraint)) {
-        writeCheckConstraint(apply, column, checkConstraint);
-      }
-    }
-  }
-
-  /**
-   * Write a check constraint.
-   */
-  protected void writeCheckConstraint(DdlBuffer buffer, Column column, String checkConstraint) throws IOException {
-
-    String ckName = column.getCheckConstraintName();
-
-    buffer.append(",").newLine();
-    buffer.append("  constraint ").append(ckName);
-    buffer.append(" ").append(checkConstraint);
-  }
-
   protected void writeCompoundUniqueConstraints(DdlBuffer apply, CreateTable createTable) throws IOException {
 
     boolean inlineUniqueWhenNull = platformDdl.isInlineUniqueWhenNullable();

src/main/java/io/ebeaninternal/dbmigration/ddlgeneration/platform/ClickHouseDdl.java

@@ -64,6 +64,11 @@ public class ClickHouseDdl extends PlatformDdl {
     return null;
   }
 
+  @Override
+  public String createCheckConstraint(String ckName, String checkConstraint) {
+    return null;
+  }
+
   @Override
   protected void writeColumnNotNull(DdlBuffer buffer) {
     // do nothing

src/main/java/io/ebeaninternal/dbmigration/ddlgeneration/platform/ClickHouseTableDdl.java

@@ -25,10 +25,4 @@ public class ClickHouseTableDdl extends BaseTableDdl {
     // do nothing
   }
 
-
-  @Override
-  protected void writeCheckConstraints(DdlBuffer apply, CreateTable createTable) {
-    // do nothing
-  }
-
 }

src/main/java/io/ebeaninternal/dbmigration/ddlgeneration/platform/MySqlDdl.java

@@ -14,6 +14,10 @@ import java.util.Collection;
  */
 public class MySqlDdl extends PlatformDdl {
 
+  // check constraint support is disabled by default. See https://groups.google.com/forum/#!topic/ebean/luFN-2xBkUw
+  // this flag is for compatibility. Use it with care.
+  private static final boolean USE_CHECK_CONSTRAINT = Boolean.getBoolean("ebean.mysql.useCheckConstraint");
+
   public MySqlDdl(DatabasePlatform platform) {
     super(platform);
     this.alterColumn = "modify";
@@ -48,11 +52,40 @@ public class MySqlDdl extends PlatformDdl {
     buffer.append("CALL usp_ebean_drop_column('").append(tableName).append("', '").append(columnName).append("')").endOfStatement();
   }
 
+  @Override
+  public String createCheckConstraint(String ckName, String checkConstraint) {
+    if (USE_CHECK_CONSTRAINT) {
+      return super.createCheckConstraint(ckName, checkConstraint);
+    } else {
+      return null;
+    }
+  }
+  @Override
+  public String alterTableAddCheckConstraint(String tableName, String checkConstraintName, String checkConstraint) {
+    if (USE_CHECK_CONSTRAINT) {
+      return super.alterTableAddCheckConstraint(tableName, checkConstraintName, checkConstraint);
+    } else {
+      return null;
+    }
+  }
+
   @Override
   public String alterTableDropConstraint(String tableName, String constraintName) {
-    // drop constraint not supported in MySQL 5.7 and 8.0 but starting with MariaDB 10.2.1 CHECK is evaluated
-    // TODO: Implement for MariaDB >= 10.2.1
-    return null;
+    // drop constraint not supported in MySQL 5.7 and 8.0 but starting with MariaDB
+    // 10.2.1 CHECK is evaluated
+    if (USE_CHECK_CONSTRAINT) {
+      StringBuilder sb = new StringBuilder();
+      // statement for MySQL >= 8.0.16
+      sb.append("/*!80016 alter table ").append(tableName);
+      sb.append(" drop check ").append(constraintName).append(" */;\n");
+      // statement for MariaDB >= 10.2.1
+      sb.append("/*M!100201 ");
+      sb.append(super.alterTableDropConstraint(tableName, constraintName));
+      sb.append(" */");
+      return sb.toString();
+    } else {
+      return null;
+    }
   }
 
   @Override

src/main/java/io/ebeaninternal/dbmigration/ddlgeneration/platform/PlatformDdl.java

@@ -213,10 +213,22 @@ public class PlatformDdl {
    */
   public void writeTableColumns(DdlBuffer apply, List<Column> columns, boolean useIdentity) throws IOException {
     for (int i = 0; i < columns.size(); i++) {
+      if (i > 0) {
+        apply.append(",");
+      }
       apply.newLine();
       writeColumnDefinition(apply, columns.get(i), useIdentity);
-      if (i < columns.size() - 1) {
-        apply.append(",");
+    }
+
+    for (Column column : columns) {
+      String checkConstraint = column.getCheckConstraint();
+      if (hasValue(checkConstraint)) {
+        checkConstraint = createCheckConstraint(maxConstraintName(column.getCheckConstraintName()),
+            checkConstraint);
+        if (hasValue(checkConstraint)) {
+          apply.append(",").newLine();
+          apply.append(checkConstraint);
+        }
       }
     }
   }
@@ -253,6 +265,13 @@ public class PlatformDdl {
     buffer.append(" not null");
   }
 
+  /**
+   * Returns the check constraint.
+   */
+  public String createCheckConstraint(String ckName, String checkConstraint) {
+    return "  constraint " + ckName + " " + checkConstraint;
+  }
+
   /**
    * Convert the DB column default literal to platform specific.
    */
@@ -494,7 +513,9 @@ public class PlatformDdl {
       if (!StringHelper.isNull(column.getCheckConstraint())) {
         String ddl = alterTableAddCheckConstraint(tableName, column.getCheckConstraintName(),
           column.getCheckConstraint());
-        buffer.append(ddl).endOfStatement();
+        if (hasValue(ddl)) {
+          buffer.append(ddl).endOfStatement();
+        }
       }
     } else {
       buffer.append(addColumnSuffix);
@@ -580,7 +601,7 @@ public class PlatformDdl {
   }
 
   protected void appendWithSpace(String content, StringBuilder buffer) {
-    if (content != null && !content.isEmpty()) {
+    if (hasValue(content)) {
       buffer.append(" ").append(content);
     }
   }
@@ -613,6 +634,13 @@ public class PlatformDdl {
     return updateNullWithDefault;
   }
 
+  /**
+   * Return true if null or trimmed string is empty.
+   */
+  protected boolean hasValue(String value) {
+    return value != null && !value.trim().isEmpty();
+  }
+
   /**
    * Null safe Boolean true test.
    */